A two-story apartment building at 166 Beach St. in Saco was slightly damaged by a fire that broke out shortly after 2 a.m. today.

No on was hurt by the fire which started in an interior stairwell, said Saco Fire Department Captain Luke Godbout.

He said the damage was estimated at about $3,500. He said firefighters quickly extinguished the fire and left the scene at about 3:30 a.m.

The cause of the blaze is under investigation.