UPDATE: Firefighters controlled the blaze in the Osborn building by mid-morning and investigators then entered the building to determine the cause and a damage estimate.

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About 100 firefighters are at the scene of a three-alarm fire at the historic Osborn building in inner Southeast Portland Friday morning.

The building, on Southeast Ash Street and Southeast Grand Avenue, houses retail and businesses on the first and second floors and apartments on the third floor, according to Portland Fire spokesman Lt. Damon Simmons. There were no injuries, he said. The cause of the fire remains under investigation.

The fire appears to have begun in the basement and spread to upper floors through voids in the walls.

Resident Danielle Higgins, who lives in one of the four apartments one the building's top floor, said she was asleep when she heard a noise. Thinking it was her alarm clock, she tried to turn it off, she said, but the noise continued.

The next thing she knew, she said, firefighters were in the building telling her and her roommate to get out. Shortly after, she heard a series of explosions as electrical transformers exploded.

"I felt bad for one of the firefighters -- he was right next to it when it blew up," she said. He was unscathed, she said.

The building has a bar, called the East End, on the first floor and work spaces on the second floor. The four apartments are on the third floor.

Higgins, a documentary filmmaker, said she is concerned for her camera gear and anxious to check if it's ok.

Police have closed SE Grand and SE Martin Luther King Jr. Boulevard for about four blocks from E. Burnside to E. Oak and TriMet's Line 6 is detouring around the area at SE Stark and the Portland Streetcar is blocked. Commuters are urged to avoid the area.

-- Stuart Tomlinson