The Boston Fire Department reports a fire called in around 4:30 a.m. at 34 Worcester Sq.  went to two alarms and sent residents into the 8-degree air.
The fire started on the second floor of the five-story building and quickly spread upwards. No residents were injured, the department says.
An MBTA bus was brought in for residents to stay in until they could find new lodgings for the day. Residents at 36 Worcester Sq. were also evacuated, although they were let back in after the fire was put out.
Fire investigators are now looking for a possible cause.