SACRAMENTO (CBS13) – Fire crews are investigating a fire at an old, vacant hotel in downtown Sacramento.

The three-alarm fire broke out in the Biltmore Hotel on J and 10th streets after 2 a.m. Thursday morning.

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Heavy smoke was seen coming from the two-story building.

Fire crews say the fire may have started in the basement.

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“These particular buildings pose a big danger to our firefighters. They are vacant. One of our biggest concerns are possibly homeless people or victims trapped inside,” said Sacramento Fire Department spokesperson Roberto Padilla.

Fire crews are checking to make sure the fire didn’t spread into any nearby buildings.

Exactly what sparked the fire is still under investigation.

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Eastbound J Street between 9th and 12th streets was closed along with 10th Street between I and K streets.