California firefighters tackled a commercial blaze that broke out at a vacant dentistry building early Thursday.

Crews responded shortly after 1:41 a.m. to multiple calls of a fire in San Bernardino, the San Bernardino County Fire Department said in an online update.

Firefighters started with an offensive attack while a search for occupants was performed. But they had to switch to a defensive posture before finishing the search.

The blaze was extinguished after 45 minutes, and no injuries were reported. The cause of the fire is under investigation.