By Ellen Wulfhorst

NEW YORK (Reuters) - Two people remained unaccounted for on Friday in the wake of an apparent gas explosion that destroyed four New York City apartment buildings and injured 19 people, police said.

The blast shook Manhattan's East Village neighborhood on Thursday afternoon, causing two buildings to collapse and burst into flames and two adjacent buildings to catch fire as well.

The blast appeared to have been gas-related, New York Mayor Bill de Blasio said. Private gas and plumbing work was going on in one of the buildings, and Con Edison utility inspectors on the scene an hour earlier had determined the work was not satisfactory.

The mayor and other officials inspected the devastated scene, where remains of the buildings were a tangled mess of bricks, wood, steel and broken glass. A few personal items were visible, including a dresser and some clothes.

Two people have been missing since the blast, officials said.

"We are looking into two individuals who are apparently unaccounted for," said a New York Police Department spokeswoman.

One of those was identified in local media as Nicholas Figueroa, 23, whose family said he had been eating lunch with a co-worker at a sushi restaurant where the explosion appeared to have originated.

His family told The New York Times that a bank statement showed he had used a debit card to pay $13.04 to Sushi Park.

Figueroa has not been heard from, his family said. His co-worker was hospitalized with injuries.

The damaged buildings comprised 49 apartments, and the American Red Cross said 90 people registered for assistance.

One of them, Naya Jones, 24, emerged from a makeshift Red Cross center carrying a stack of folded white towels. Displaced by the blast, she said she spent the night at a YMCA and voiced concern for the injured victims.

"It could have been me," she said.

Firefighters were searching through rubble that was still burning, said a fire department spokesman. "We're putting out smoldering debris," he said.

Two buildings entirely collapsed, a third mostly collapsed and will have to be razed and the fourth had severe fire damage but was structurally sound, according to fire officials.

Con Edison said its inspectors had evaluated a gas service upgrade installed in the building that exploded and found it failed inspection partly because there was insufficient space for installation of a meter in the basement.

(Additional reporting by Sebastien Malo, Editing by Susan Heavey and Will Dunham)