More than 25 fire and rescue vehicles responded to a three-alarm fire which spread through three floors of the Mather Court apartment building yesterday afternoon.

Nobody was injured in the blaze, which began on the first floor of the building at 1 Waterhouse St. The fire skipped the second floor, but spread to the third floor and part of the fourth floor.

The fire was a concealed fire, in that it spread behind the walls and, as a result, could not be seen.

Although the cause of the fire is still unknown, Cambridge Deputy Fire Chief Jerry Rearden said it was most likely an accident, probably related to a plumbing problem on the first floor.

Firefighters said the fire was reported to the Cambridge Fire Department at approximately 1:40 p.m. and was under control by 2:55 p.m.

All building residents, most of whom are elderly, evacuated quickly and safely through the building's interior, according to Cambridge Fire Department Captain Michael Morrissey.

"It is better to deal with a fire like this in the daytime instead of at night because it's easier to evacuate people," Morrissey said.

But, firefighters said that many pets--including a cat in a third floor apartment--were not rescued until several hours after the fire began.

Battling the fire required ten Cambridge pumping engines and five hook-and-ladder trucks. They were aided by two engines from the Somerville and Boston fire departments.

The Garden Street site was cluttered with ambulances, air supply vehicles and an arson investigation crew. Despite the overwhelming number of vehicles present, however, Morrissey said the fire was of average size.

Traffic was stopped on Garden Street across from the Sheraton Commander hotel as a police officer directed traffic onto nearby Mason Street. Traffic did not resume moving on Garden Street until 3:20 p.m., when the fire engines began to leave.

According to Rearden, firefighters face particular difficulties when confronted with a fire concealed in the walls of a building, because it is hard to control. In order to locate the fire, they need to tear out the walls, he said.

"It takes a lot of personnel, and a lot of work real quick to get it cut off," said one member of the Cambridge Fire Department's Fire Investigation Unit.