NEW YORK (AP) _ Firefighters and rescue workers combed through the rubble of two collapsed buildings early Wednesday looking for three people feared trapped in the pile of bricks and wood.

``We're hoping to find someone who might have been caught in a spot where there was some air,'' Fire Commissioner Thomas Von Essen said.

A four-story brownstone apartment building on a quiet Brooklyn street collapsed Tuesday night, bringing down much of an adjacent three-story structure. Only three of the six people who lived in the buildings were accounted for.

Kenneth Dinham, who works at a drug treatment facility across the street, said he heard an explosion ``just like a bomb went off.''

``I came outside, all I could see was smoke in the air,'' Dinham said. ``The windows moved, the place shook.''

The cause of the accident was not immediately known, though Mayor Rudolph Giuliani said a gas explosion might have caused it. KeySpan Energy workers examined pipes outside the buildings and found no evidence of a gas leak, a company spokesman said.

The roof of the first building fell without breaking, making it more difficult for rescue workers to look for survivors underneath. Cameras were being used to check under the debris.

Two tenants were treated at a hospital, but their injuries did not appear to be life-threatening, fire officials said. Two firefighters were treated for minor injuries.

Rescue workers said the missing people were the owners of one building and a tenant in the other.

Neighbor Kristen Austin said she knew a couple who lived in one of the buildings and that a firefighter confirmed they were inside.

``A couple of other neighbors and I just want to start pulling rubble and calling their names to let them know people care,'' Austin said. ``We're sort of praying they wound up in the basement or something, protected.''