PHILADELPHIA (CBS) — A Center City apartment building was evacuated early Wednesday morning after it filled with smoke from an underground electrical fire.

The incident occurred around 3:30 a.m. at the ten-story Oakwood apartment building along the 1600 block of Sansom Street.

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PECO was working to figure out the exact location of the problem.

“There’s a series of wires that run under this building,” says Lieutenant Bernard Gilliam, “so it’s a little difficult sorting out exactly where the problem comes from.”

Firefighters were checking the building floor by floor and more than three dozen residents were evacuated as a precaution.

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No injuries were reported, but the incident did leave a few hundred PECO customers without power along the 1500 and 1600 hundred blocks of Sansom Street, and the 100 and 200 blocks of 16th Street.

As of 3 p.m., 46 customers remained without power. PECO said it expects to restore power to all of them by 8 p.m. Wednesday.

The American Red Cross Southeastern PA will be opening a reception center at Greenfield Elementary School at 22nd and Chestnut for anyone displaced by the fire. It’s unclear how many people have been affected or are expected at the school.

The incident also caused several street closures in the area. 16th Street was blocked between Chestnut and Sansom Streets. Sansom Street was closed from 15th to 17th Streets.

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There were reports of an odor of gas in the area, but officials say it was only the release of a small amount of trapped gas from a previous repair unrelated to the fire.