Four residential buildings in New York's East Village neighbourhood have caught fire from an apparent gas explosion and three have collapsed, injuring 19 people, authorities have said.

The blast shortly after 3pm local time on Thursday sent flames leaping into the sky and rocked the residential area in Manhattan. Bloodied victims ran from the buildings, collapsing on the street, witnesses said.

New York Mayor Bill de Blasio said that preliminary evidence indicated it was a gas-related explosion.

Nineteen people were hurt. Four, all civilians, were in critical condition, a Fire Department spokesman said.

A New York police spokesman said there were no reports of anyone missing.

Failed inspection

The Con Edison utility said in a statement that its inspectors had been at the site on Thursday to evaluate work a plumber was doing in a building for a gas service upgrade. The work failed to pass inspection, it said.

The seven-alarm blaze in the neighbourhood of small businesses, restaurants and apartments involved more than 250 Fire Department personnel.

Moishe Perl, 64, who owns Moishe's Bake Shop nearby, said he heard an explosion, ran outside and saw the lower floors of a building start to crumble.

"Most of the people were running out of the building and climbing down the fire escape," he said, while others were helped out of windows by passersby.

Ben Mackinnon, 28, said he was drinking coffee in a cafe when he heard an explosion from across the street.

"The explosion was big enough that the door of the cafe blew open," Mackinnon said.

He said he saw several bloodied men emerge from a sushi restaurant where the explosion appeared to originate. One of them fell to the pavement.

Shameem Noor, a cashier at the Veselka restaurant about a block away, said he heard the blast and saw three or four people fall to the street.

The four buildings contain 49 flats, according to a spokesman for the American Red Cross at the scene. The ground floors were occupied by small eateries.

A relocation centre for displaced residents was set up in a nearby elementary school, the Red Cross spokesman said.

Source: Agencies