SAN FRANCISCO (CBS SF) — Eight construction workers were hospitalized with smoke inhalation after a three-alarm fire broke out at a building undergoing renovations near San Francisco’s United Nations Plaza Monday afternoon, a fire spokeswoman said.

The blaze was reported at 12:03 p.m. at 45 McAllister St., the site of the former Renoir Hotel.

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About two dozen construction workers were in the eight-story building doing welding work when the fire started on the fifth floor, according to KCBS’ Mike Sugarman who is at the scene.

Hundreds were evacuated safely, but eight were taken to the hospital with smoke inhalation.

About 80 firefighters responded and initially went into the structure, but evacuated after hearing explosions that possibly came from propane tanks inside the building.

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The fire was reported as reaching a five-alarm response but officials later downgraded the blaze to three alarms.

Fire crews are fighting the flames from the outside and the blaze is not expected to be extinguished until later this afternoon, Talmadge said.

The response to the fire has shut down a portion of Market Street as well as other streets surrounding the building.

The cause of the fire has not yet been determined.

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