Investigation underway after crews extinguish large fire at Irvine commercial building

It took dozens of firefighters nearly three hours to extinguish a massive fire burning at a commercial building in Irvine on Saturday. 

The blaze was reported at around 2:30 p.m. in the 1700 block of Kettering Street, located between Gillette Avenue and Armstrong Avenue, according to the Orange County Fire Authority. 

Crews arrived and found much of the building already engulfed in flames, they said. As such, they declared the blaze a Third Alarm and began to battle in defensive mode, from outside and from the ground. 

So far there have been no reports of injury. 

Arson investigators were called to the scene to determine what sparked the blaze. 

Firefighters say they're unsure what type of business was located inside of the building.