Six-alarm fire in a Berkeley building under construction on University Avenue.

A large fire burned down in a building in downtown Berkeley on Saturday night, authorities said.

Firefighters responded to a six-alarm fire just before 6:30 p.m. at 2067 University Avenue, according to the Berkeley Police Department.

The building was under construction.

The fire spread to an adjacent occupied building, which had to be evacuated, said Dave Brannigan, a spokesperson for the Berkeley Fire Department. Firefighters were able to prevent the blaze from causing significant damage to the building.

“We stopped this pretty quickly,” he said.

At around 9:30 p.m., the fire was confined to the original building where it started, but it continued to burn and will likely burn overnight, Brannigan said.

“It’s probably going to be a long night,” he added.

A cause of the fire has not yet been determined.

University Avenue was closed between Milvia Street and Shattuck Avenue.

No injuries were reported.

PG&E’s outage map showed that around 250 customers were without power in the area, but it was not clear whether the outages were related to the fire.

Sarah Ravani is a writer for the San Francisco Chronicle. Email: [email protected] Twitter: @SarRavani