Firefighters were investigating the cause of a two-alarm fire that damaged a unit Saturday in a three-story building in Makiki.

The fire started at about 2:45 p.m. in apartment 31 on the third floor of 1327 Pensacola St.

Honolulu Fire Department Battalion Chief Geoffrey Chang said a woman smelled smoke and looked outside to see black smoke and flames coming from the apartment next door.

Nine fire companies and about 30 firefighters responded and contained the fire within 16 minutes of the initial call. The fire was extinguished at 3:07 p.m.

The single resident of the one-bedroom apartment was not at home at the time, and it was not clear if he would be able to stay in the apartment. No one was hurt and no other units were damaged.

Chang said the fire appeared to have started in a back room, and a fire investigator was searching for a cause and damage estimate.

A resident who lives on the first floor of the building said his landlord told him the fire started from an air conditioner that was left running while the resident was away.

Paul Minczer, who lives in a high-rise behind the building, said he heard the alarms and went to his fire escape to see flames coming out of the unit’s back lanai and rising above the roof edge by about 3 feet.

Chang noted the apartment did not have a smoke detector and there were no early warnings of the fire. He urged all residents to have a smoke detector in their home.