EVERETT, Wash. -- Firefighters battled a 2-alarm fire that broke out at an apartment complex on Friday afternoon.

Firefighters responded to the blaze at the Copper Stone Apartments in the 400 block of 85th Place SW around 4:20 p.m.

Pictures taken from Air 4 showed firefighters on the smoky roof trying to douse the flames that were burning inside the building's south end.

A top-level unit of the three-story complex appeared to be badly damaged, but the extent of the damage was not immediately clear.

Firefighters said the blaze appears to have started in the lower area of a stairwell that serves six of the 18 units and quickly spread upward. The cause of the fire was not known.

Firefighters initially believed some people were trapped inside the building; however, they did not find anyone inside.

Units from Naval Station Everett also responded to the blaze.

There were no reports of injuries.

The power to the building was to remain off overnight, and the Red Cross was called in to aid the displaced residents.