BOSTON — Four people were rescued and taken to a hospital Wednesday after a fire at a 10-story Boston condominium building, fire officials said.

Investigators believe the blaze at a building in Boston’s Back Bay began in a seventh-floor unit with smoke quickly spreading to the eighth floor, said Boston Fire Chief Ronald Keating.

He said the cause of the fire remains under investigation.

After firefighters arrived to the scene, Keating said residents on the lower floors escaped down stairways while residents on the top three floors were brought to the roof of the building that is more than 100 years old.

“We had a tremendous amount of difficulty moving inside the building because the building is so old,” with narrow stairways, said Keating, after the fire was put out.

It was unclear how many of the building’s 174 residents were home when the fire broke out in the early afternoon; Keating said many of them are college and university students. Four residents were being evaluated at a hospital, but their conditions were not immediately known.

Commissioner Roderick Fraser said one firefighter also was taken to a hospital after complaining of chest pains.

Keating said the building had no sprinklers since it was built before they were required.

The blaze was the first time in several years the department had struck nine alarms for a fire, department spokesman Steve MacDonald said. Officials said they did so as a precaution to make sure there was sufficient manpower at the scene.