Seven people died and over 60 injured in the explosion which leveled two residential buildings in New York's East Harlem neighborhood, a Fire Department of New York spokesman told Xinhua.

The four more bodies were pulled from rubble between midnight Wednesday and Thursday morning and so far at least nine are still missing.

Using backhoes and a bulldozer, crews worked through the night under bright searchlights in the hope of finding someone alive, with firefighters still putting out hot spots at the explosion site in uptown Manhattan.

"This is a difficult job, a challenging job," the spokesman said, calling it "a very terrible and traumatic scene."

The blast struck a building at uptown Manhattan's East Harlem neighborhood at about 9:30 a.m. (1330 GMT) Wednesday, blowing out windows in surrounding buildings and sending debris crashing down onto nearby streets.

Two five-story residential buildings next to each other collapsed, with one essentially gone from the blast. Preliminary investigation suggested that the only warning before the blast was a call about a gas leak.

Utility company Con Edison said it received the call from a resident in an adjacent building about 15 minutes before the explosion. The company said it sent two workers to the scene after the call, but they arrived two minutes after the explosion.

In a media briefing more than two hours after the explosion, Mayor Bill de Blasio said that the explosion was caused by a gas leak with a heavy fire ensuing.

As debris falling onto the nearby train tracks, Metro-North service was halted Wednesday until the middle of the evening.