NEW YORK (AFP) - Two people were missing Friday from a sushi restaurant after an explosion flattened three buildings and ravaged a fourth property in New York's East Village, injuring 22 people, officials said.

The explosion blew the front off a commercial and residential property on Second Avenue on Thursday, minutes after the owner of the restaurant smelled gas and telephoned the landlord.

The gas-fuelled fire grew rapidly, eventually bringing down three properties and badly damaging a fourth, with the fire still smouldering Friday.

If investigators conclude gas was the cause, it would be the second such explosion to bring down residential property in New York in a year after eight people were killed in Harlem in 2014.

"We have two people that we know for sure are unaccounted for and there may be more," said New York Mayor Bill de Blasio.

Police said witness statements put both missing people in the sushi restaurant at the time of the explosion. Local media identified them as a young man on a date and a busboy.

Fire Commissioner Daniel Nigro said it would take a week to remove the debris.

"We will treat the scene as if people are there," he said.

In total 22 people were injured, including six uniformed personnel and four civilians in a critical condition, officials said.

De Blasio said three buildings had collapsed and the fourth was very seriously damaged by fire. Besides the sushi restaurant, a shop selling Belgian frites was also destroyed.

"The strong assumption is it's a gas explosion," the mayor said, adding it was possible that a gas line had been "inappropriately accessed internally by people in the building."

Engineer inspectors from power company Con Edison examined piping in one of the buildings earlier in the day. Fifteen minutes after they left, the owner of the sushi restaurant smelled gas.

He called the landlord, who called a contractor. The explosion occurred as the landlord's son and the contractor went to the basement. Both sustained burns to the face, officials said.

Dramatic cell phone footage broadcast by TV channel PIX11 showed panicked people running in fear from the sushi restaurant.

"What happened? Oh my God!" one woman is heard yelling. Bystanders bend over a person lying amid debris.

The Red Cross set up an emergency site in a school to support those made homeless and a hotel also offered three free nights to people living in the immediate vicinity.

Eight people were killed when a gas explosion leveled two apartment buildings in East Harlem in Manhattan on March 12, 2014.

The East Village is one of the most popular areas of New York, home to a large number of students and wealthy professionals, and stuffed with boutiques, restaurants, nightclubs and cafes.