Four people were forced out of their apartment overnight, on the second floor of a Lancaster building.
Now, Lancaster police are trying to figure out how the fire started.
Firefighters were called to the building on Central Avenue, around 1:30 a.m. Thursday.
There are businesses on the first floor and apartments on the second floor.
No one was hurt.
It's unclear if the businesses on the first floor were affected.
Firefighters do not believe this fire is suspicious.