A major explosion caused by a gas leak has flattened two Manhattan apartment buildings in a fireball, killing at least four people and injuring 63 others.
New York Mayor Bill de Blasio called the incident on Wednesday "a tragedy of the worst kind" and his office said nine residents from the two collapsed buildings were still unaccounted for by nightfall.
Firefighters battled throughout the afternoon to extinguish the heavy fire in East Harlem, where witnesses compared the scene of twisted metal, thick white smoke and dusty rubble to a war zone.
Late on Wednesday the death toll was raised from three to four, said US media outlets CNN, ABC and CBS.
The explosion sparked inevitable reminders for some New Yorkers of the 9/11 terror attacks in 2001 that brought down the Twin Towers. Other witnesses said it felt like an earthquake.
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There were 15 apartments in the two buildings that collapsed, de Blasio and city officials told reporters near the scene at 116th Street and Park Avenue, a mainly Latino community.
Around 15 minutes before the blast, energy company Con Edison received a call from an adjoining apartment building alerting maintenance staff to the smell of gas.
The explosion struck around 9:30 am (1330 GMT) and the New York Fire Department said firefighters were on the scene two minutes later.
"There was a major explosion that destroyed two buildings. The explosion was based on a gas leak," de Blasio said.
The Mexican Foreign Ministry said two women who were among the dead were Mexicans, along with one of those injured.
Lamenting the "deeply unfortunate incident," the ministry said in a brief statement that Mexican consular staff remain in close contact with New York authorities.
Four different hospitals said they treated a total of 63 patients, the vast majority with minor injuries.
Hundreds of police and more than 250 firefighters were on site with emergency trucks, as a dense column of smoke spewed into the sky over the Metro-North railway line.
The blast forced the suspension of train services in and out of Grand Central Station in midtown Manhattan for part of the day.
Jazzmen Arzuaga, 30, said she was at work at a hospital when her wife rang to tell her what had happened.
"She called me and told me 'Oh my God, you need to come home now, it's like World War II, people are dying, there was an explosion.' I just literally ran," she said.
The couple live across the street from the blast.
Arzuaga's wife Jay Virgo, also 30, said she was lying in bed when the blast threw her to the floor.
"There was glass everywhere, huge pieces of glass. It just looked crazy," she said.
Con Edison confirmed that a resident reported smelling gas inside the apartment building at 1652 Park Avenue.
"Our crews are checking our gas lines and working to isolate any leaks that they find and they're working closely with the FDNY to make the area safe," company spokesman Bob McGee said.
