Fire broke out early Wednesday in a top‑floor apartment of downtown Santa Rosa’s historic Rosenberg Building, trapping a female resident who was rescued by firefighters, displacing five and forcing the evacuation of the large building, according to Santa Rosa fire officials.

The woman, believed to be 35 years, was taken to Santa Rosa Memorial Hospital for smoke inhalation treatment.

The fire’s origin was traced to an electrical issue from a power strip extension cord — including one plug used for a pet lizard’s heat lamp, said Battalion Chief Matt Dahl.

Several people reported the fire just before 12:50 a.m., warning firefighters that one person appeared trapped. A Santa Rosa fire engine already was out on a call and the crew arrived within one minute, finding several residents spilling out into the street and sidewalk, some with wheelchairs and walkers.

The large Mendocino Avenue building, built in 1921 just off Old Courthouse Square, now is home to 77 subsidized low-rent apartments. There was no sign of fire from outside but firefighters found smoke on the sixth floor and a fire in an apartment there. The flames mostly had been doused by the apartment’s sprinkler system but the residence was smoky, hindering the woman’s ability to get out, Dahl said. Firefighters helped her down to an ambulance and evacuated others on the fifth and sixth floors.

The flames hadn’t spread to other apartments but there was water damage from sprinklers to four apartments and Dahl estimated the overall loss at $100,000.

The Red Cross and building property manager arranged temporary accommodations for residents of the five damaged apartments, Dahl said.

Three dozen Santa Rosa and Sonoma County Fire firefighters responded with seven engines and two ladder trucks — a show of force due to the size of the building and the need for evacuations. The effort wrapped up about 3 a.m.

The Rosenberg Building originally was the tallest structure north of San Francisco and has been a downtown Santa Rosa landmark for almost 100 years. About 30 years ago it was converted to apartments and sprinklers were added.

Santa Rosa Assistant Fire Marshal Ian Hardage said the sprinklers likely saved the building from a much larger fire and may have saved lives. It saved at least one, Hardage said — the lizard.

You can reach Staff Writer Randi Rossmann at 707‑521-5412 or randi.rossmann@pressdemocrat.com. On Twitter@rossmannreport.