SAN DIEGO — An arson investigation is underway Friday after an office building in Normal Heights caught fire, the San Diego Fire-Rescue Department confirmed.

The fire was first reported around 7 a.m. on the second story of an office building located at 3288 El Cajon Boulevard.

Just before 7:30 a.m., crews had knocked down the fire, which caused visible damage to the outside of the office.

There was nobody inside the office unit at the time of the fire and there were no injuries reported, SDFD said.

Investigators with the SDFD metro arson strike team me were called to the scene to determine the cause of the fire.