PHOTOS: Building explosion in Upper Manhattan kills at least six

Emergency crews respond to an explosion that leveled two apartment buildings in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. The blast happened after a neighbor reported smelling natural gas. (AP Photo/Jeremy Sailing) ( NYC Explosion )

Firefighters work the scene of an explosion that leveled two apartment buildings in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. Con Edison spokesman Bob McGee says a resident from a building adjacent to the two that collapsed reported that he smelled gas inside his apartment, but thought the odor could be coming from outside. (AP Photo/Jeremy Sailing) ( APTOPIX NYC Explosion )

People run after an explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. T (AP Photo/Jeremy Sailing) ( APTOPIX NYC Explosion )

Emergency workers respond to the scene of an explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/Jeremy Sailing) ( NYC Explosion )

Police move people away from the scene of an explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/Jeremy Sailing) ( NYC Explosion )

Emergency crews respond to an explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. The explosion leveled an apartment building, and sent flames and billowing black smoke above the skyline. (AP Photo/Jeremy Sailing) ( NYC Explosion )

Firefighters from the Fire Department of New York (FDNY) respond to a 5-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. Reports of an explosion were heard before the collapse of two multiple-dwelling buildings that left at least 11 injured. (Photo by Andrew Burton/Getty Images) ( 478132919 )

Police respond to the scene of an explosion that leveled two apartment buildings in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/Jeremy Sailing) ( APTOPIX NYC Explosion )

Firefighters try to put out a fire after a reported explosion and building collapse in the Harlem area of New York City, New York, USA, 12 March 2014. The cause of the explosion, as well as reports of any injuries, had not yet been determined. EPA/JUSTIN LANE ( USA NEW YORK FIRE )

A ladder truck pours water as the Fire Department of New York (FDNY) respond to a 5-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. Reports of an explosion were heard before the collapse of two multiple-dwelling buildings that left at least 11 injured. (Photo by Andrew Burton/Getty Images) ( 478132947 )

Firefighters respond to a fire on 116th Street in Harlem after a building exploded in huge flames and billowing black smoke, leading to the collapse of at least one building and several injuries, Wednesday, March 12, 2014, in New York. (AP Photo/John Minchillo) ( NYC Explosion )

Firefighters try to put out a fire after a reported explosion and building collapse in the Harlem area of New York City, New York, USA, 12 March 2014. The cause of the explosion, as well as reports of any injuries, had not yet been determined. EPA/JUSTIN LANE ( USA NEW YORK FIRE )

Police move people away from the scene of an explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/Jeremy Sailing) ( NYC Explosion )

A view of firefighters on the scene where a group of buildings were damaged nu an explosion in New York, New York, USA, 12 March 2014. EPA/JUSTIN LANE ( USA NEW YORK FIRE )

In this image taken from video from WABC, firefighters battle a blaze at the site of a possible explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/WABC-TV) ( NYC Explosion )

Alecia Thomas, left, is comforted by her friend, Shivon Dollar, after she lost her home following an explosion that leveled two apartment buildings in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/Mark Lennihan) ( APTOPIX NYC Explosion )

In this image taken from video from WABC, firefighters battle a blaze at the site of a possible explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/WABC-TV) ( NYC Explosion )

Firefighters from the Fire Department of New York (FDNY) respond to a 5-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. Reports of an explosion were heard before the collapse of two multiple-dwelling buildings that left at least 11 injured. (Photo by Andrew Burton/Getty Images) ( 478132985 )

Firefighters from the Fire Department of New York (FDNY) respond to a 5-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. Reports of an explosion were heard before the collapse of two multiple-dwelling buildings that left at least 11 injured. (Photo by Andrew Burton/Getty Images) ( 478132995 )

In this image taken from video from WABC, firefighters battle a blaze at the site of a possible explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/WABC-TV) ( NYC Explosion )

Bystanders cover their faces from smoke as they watch the scene of an explosion and building collapse at Park Avenue and East 116th Street March 12, 2014 in the Harlem section of New York. AFP PHOTO/Stan HONDA/AFP/Getty Images ( 527994056 )

Firefighters on the scene where a group of buildings were damaged by fire and a possible explosion in New York, New York, USA, 12 March 2014. EPA/ANDREW GOMBERT ( USA NEW YORK FIRE )

In this image taken from video from WABC, firefighters battle a blaze at the site of a possible explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/WABC-TV) ( NYC Explosion )

Heavy smoke pours from the debris as the Fire Department of New York (FDNY) responds to a 5-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. Reports of an explosion were heard before the collapse of two multiple-dwelling buildings that left at least 11 injured. (Photo by Andrew Burton/Getty Images) ( 478132785 )

A police officer tries to push back the crowd of people near the scene where a group of buildings were damaged by fire and a possible explosion in Harlem, New York City, New York, USA, 12 March 2014. EPA/JUSTIN LANE ( USA NEW YORK FIRE )

Rescue workers remove an injured person on a stretcher following a building explosion and collapse in East Harlem, Wednesday, March 12, 2014 in New York. (AP Photo/Mark Lennihan) ( NYC Building Collapse )

Firefighters from the Fire Department of New York (FDNY) respond to a 5-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Andrew Burton/Getty Images) ( 478133591 )

Firefighters from the Fire Department of New York (FDNY) respond to a 5-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Andrew Burton/Getty Images) ( 478133549 )

Seen from behind the Metro North elevated train line, firefighters from the Fire Department of New York (FDNY) respond to a 5-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Andrew Burton/Getty Images) ( 478133753 )

In this photo provided by Shane Kennedy, smoke rises from the site of an explosion and building collapse near Park Avenue and 116th Street in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/Shane Kennedy) ( NYC Explosion )

Firefighters respond to a fire on 116th Street in Harlem after a building exploded in huge flames and billowing black smoke, leading to the collapse of at least one building and several injuries, Wednesday, March 12, 2014, in New York. (AP Photo/John Minchillo) ( NYC Explosion )

Rescue workers remove an injured person on a stretcher after a possible explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014 (AP Photo/Mark Lennihan) ( NYC Building Collapse )

A crowd watches from behind a barricade as emergency personnel respond to a 5-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Andrew Burton/Getty Images) ( 478139519 )

Smoke rises from a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Justin Heiman/Getty Images) ( 478140151 )

Debris sits on roof during a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Justin Heiman/Getty Images) ( 478140589 )

Firefighters from the Fire Department of New York (FDNY) respond to a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Justin Heiman/Getty Images) ( 478140617 )

Firefighters from the Fire Department of New York (FDNY) respond to a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Justin Heiman/Getty Images) ( 478140663 )

Emergency personnel stand on the Metro-North train tracks as they respond to a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Justin Heiman/Getty Images) ( 478147785 )

A firefighter from the Fire Department of New York (FDNY) walks on a roof during a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Justin Heiman/Getty Images) ( 478147939 )

Firefighters from the Fire Department of New York (FDNY) respond to a five-alarm fire and building collapse at 1646 Park Ave as a drone flies overheard in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Justin Heiman/Getty Images) ( 478148321 )

Firefighters from the Fire Department of New York (FDNY) respond to a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Justin Heiman/Getty Images) ( 478148529 )

Bystanders cover their faces against the smoke as they watch the scene of an explosion and building collapse at Park Avenue and East 116th Street March 12, 2014 in the Harlem section of New York. AFP PHOTO/Stan HONDA/AFP/Getty Images ( 527994100 )

People stand behind a police line at the scene where a group of buildings were damaged by an explosion in New York, New York, USA, 12 March 2014. EPA/ANDREW GOMBERT ( USA NEW YORK FIRE )

Firefighters and a police officer on the scene where a group of buildings were damaged by fire and a possible explosion in New York, New York, USA, 12 March 2014. EPA/ANDREW GOMBERT ( USA NEW YORK FIRE )

A New York City police officer, left, tells Brian Wilson, center, to land the drone that he was flying over the scene of an explosion that leveled two apartment buildings in East Harlem, Wednesday, March 12, 2014 in New York. Wilson says he uses the aerial drone to document buildings, weddings and news events. (AP Photo/Mark Lennihan) ( NYC Explosion )

Mayor Bill de Blasio, center, arrives to visit the site of an explosion that leveled two apartment buildings in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. Con Edison spokesman Bob McGee says a resident from a building adjacent to the two that collapsed reported that he smelled gas inside his apartment, but thought the odor could be coming from outside. (AP Photo/Bebeto Matthews) ( NYC Explosion )

Passersby watch as rescue efforts continue after an explosion and building collapse in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (AP Photo/Mark Lennihan) ( NYC Explosion )

A man receives medical attention after an explosion that leveled two apartment buildings in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. The blast happened after a neighbor reported smelling natural gas. (AP Photo/Bebeto Matthews) ( NYC Explosion )

An injured man (L) is assisted by NYFD emrgency medical services personell near the scene of an explosion and building collapse at Park Avenue and East 116th Street March 12, 2014 in the Harlem section of New York. AFP PHOTO/Stan HONDA/AFP/Getty Images ( 527992174 )

New York City Fire Department firefighters at the scene of an explosion and building collapse at Park Avenue and East 116th Street March 12, 2014 in the Harlem section of New York. AFP PHOTO/Stan HONDA/AFP/Getty Images ( 527993998 )

Bystanders watch the scene of an explosion and building collapse at Park Avenue and East 116th Street March 12, 2014 in the Harlem section of New York. AFP PHOTO/Stan HONDA/AFP/Getty Images ( 527994017 )

n this image handout provided by the Office of Mayor of New York, firefighters from the Fire Department of New York (FDNY) pour water on the rubble as they respond to a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Rob Bennett/Office of Mayor of New York/Getty Images) ( 478167113 )

In this image handout provided by the Office of Mayor of New York, firefighters from the Fire Department of New York (FDNY) walk in the rubble as they respond to a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Rob Bennett/Office of Mayor of New York/Getty Images) ( 478166879 )

In this image handout provided by the Office of Mayor of New York, firefighters from the Fire Department of New York (FDNY) respond to a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Rob Bennett/Office of Mayor of New York/Getty Images) ( 478166877 )

In this image handout provided by the Office of Mayor of New York, firefighters from the Fire Department of New York (FDNY) walk in the rubble as they respond to a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Rob Bennett/Office of Mayor of New York/Getty Images) ( 478166871 )

A man receives medical attention near the site of an explosion that leveled two apartment buildings in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. Con Edison spokesman Bob McGee says a resident from a building adjacent to the two that collapsed reported that he smelled gas inside his apartment, but thought the odor could be coming from outside. (AP Photo/Bebeto Matthews) ( NYC Explosion )

A man is loaded into an ambulance on a stretcher hours after a two-building collapse on March 12, 2014 in New York City. (Photo by Andrew Burton/Getty Images) ( 478205965 )

Water is sprayed on smoldering debris from a two building collapse on March 12, 2014 in New York City. (Photo by Andrew Burton/Getty Images) ( 478221321 )

Firefighters from the Fire Department of New York (FDNY) respond to a five-alarm fire and building collapse at 1646 Park Ave in the Harlem neighborhood of Manhattan March 12, 2014 in New York City. (Photo by Kena Betancur/Getty Images) ( 478205341 )