It could take a week, working around the clock, to comb through the rubble of Thursday's apparent gas explosion that destroyed three lower Manhattan apartment buildings and injured 22 people, FDNY Commissioner Daniel A. Nigro said Saturday.

"It's going to be slow and arduous to dig out, search through the rubble," Nigro said after visiting a firehouse near the blast with Mayor Bill de Blasio. "They're searching very carefully, so it'll be a week's operation, day and night for us to go through it. We're still looking for two missing persons."

Authorities Saturday used heavy equipment to continue to move the rubble, and cadaver dogs sniffed for signs of life or human remains. Officials have identified the missing men as Nicholas Figueroa and Moises Lucon, both 23. They were in a sushi restaurant on the ground floor at 121 Second Ave. when the building collapsed shortly after 3 p.m. Thursday.

Lucon, who moved to New York City about six years ago from Guatemala, worked at the restaurant. Figueroa, who worked at a bowling alley at Chelsea Piers, was on a blind date at the time of the explosion, his family said.

American Red Cross workers supplied snacks to the crews sifting through the rubble and comforted a man identified as Lucon's brother a block from the scene. The man, overcome with emotion, cried and cupped his face with his hands near a Red Cross van.

De Blasio said on Friday that someone may have "inappropriately accessed" a gas line at the site, causing the explosion and fire that triggered the collapse of three five-story buildings and damaged a seven-story building.

State and city authorities are continuing to investigate the cause.

advertisement | advertise on newsday

The mayor said Friday the owner of the sushi restaurant smelled gas just 15 minutes before the blast but called the landlord instead of authorities.

On Saturday, de Blasio visited and thanked firefighters in Engine Company 33 and Ladder 9, the lower Manhattan firehouse that was the first to respond to the blast site. De Blasio also thanked Michael Shepherd, 47, a decorated firefighter with Squad 41 in the South Bronx who, though off-duty, helped to rescue victims of the explosion.

"This is truly heroic. You have a dad who's a real hero," de Blasio told Shepherd's 10-year-old son, Michael Patrick.

With Kevin Deutsch,

Matthew Chayes and AP