Dennis Fire Chief Mark Dellner said they believe the fire may have started in a first floor unit with an overturned candle, but that cause has not been confirmed.
Three or four people had to jump from second floor windows to get out of the building in time. Injuries from those who jumped to safety included broken bones and internal injuries, according to Dellner.
The fire sent 12 people to area hospitals, including fire and police personnel.
Dellner said the damage to the building could have been worse. He said the efforts of the six fire departments involved saved about half the building and about $1 million in damages.