Two people are missing after an explosion brought down three buildings and damaged a fourth property in New York's popular East Village, injuring 25 people, city officials say.

Preliminary indications suggest Thursday's blast, which triggered a fire that lingered into a second day, was gas-related, raising fresh concerns about safety in some of Manhattan's older buildings.

Police listed two people as unaccounted for early on Friday. Local media identified them as a young man on a date at a sushi restaurant, in the building where the explosion happened, and a restaurant worker.

Twenty civilians and five uniformed personnel were injured, city hall officials said, raising an earlier injury toll of 19.

Four civilians were taken to the hospital in a critical condition.

The blast ripped through a commercial and residential building at 121 Second Avenue, triggering its partial collapse and the partial collapse and full collapse of two adjoining properties.

City hall said that all three buildings were destroyed, as any remaining portions would have to be knocked down.

Fire personnel were still working to extinguish the fire after daybreak on Friday, officials said.

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.

New York Mayor Bill de Blasio said the initial impact appeared to have been caused by plumbing and gas work at the site.

Last year, eight people were killed when a gas explosion levelled two apartment buildings in East Harlem in northern Manhattan on March 12, 2014.