NEW YORK - Searching with hands and dogs through scoops of rubble from three apartment buildings leveled in an apparent gas explosion, emergency workers painstakingly looked for signs of two missing people Saturday, though authorities acknowledged the chances were slim.

Meanwhile, investigators worked to piece together exactly what caused the blast that injured 22 people in Manhattan's East Village. Officials estimated it could take a week of 24-hour-a-day work to sift through the heap of loose brick, wood, and debris.

"It's going to be slow and arduous," Fire Commissioner Daniel Nigro said Saturday. Emergency workers were using heavy machinery to dig out rubble and place it in the street, where each scoop is examined manually and sniffed by dogs, he said. Detectives issued posters seeking information on the whereabouts of two men believed to have been in the sushi restaurant on the ground floor of one of the collapsed buildings: Moises Lucon, 26, who worked at the restaurant, and Nicholas Figueroa, 23, a bowling alley worker who had been there on a date.

Their families showed their photos and asked for help.

"We have just been walking down the streets, one by one," brother Zacarias Lucon told the Daily News of New York. "We are just so exhausted and upset."

Figueroa's relatives said they were holding out hope. "My brother is strong," Neal Figueroa told reporters.

But hope was dimming. Asked about whether anyone would have survived, city Emergency Management Commissioner Joseph Esposito said: "I would doubt that very seriously."

As of Saturday, no one else was believed to be missing related to the explosion, which sparked a raging blaze that took hundreds of firefighters to quell. Mayor Bill de Blasio visited a firehouse Saturday to thank some of them.