SAN FRANCISCO -- A firefighter was injured early Thursday when a massive façade crashed down on him as he helped battle a three-alarm warehouse fire that may have housed an illegal indoor pot farm, authorities said.

Fire was first reported at around 4:45 a.m. in a single-story warehouse building near Industrial Street and Revere Ave. in the city’s Bayview District, according to SF fire spokeswoman Lt. Mindy Talmadge.

“It’s pretty incredible, especially warehouse fires,” Talmadge said of the blaze. “They are large open structures on the inside so there can be a lot of fire before it appears. This was a very visual fire.”

The blaze grew quickly from one alarm to three alarms as 135 firefighters fought the blaze.

It also turned into a very dangerous fire to fight.

During the height of the blaze a 20-foot high façade came crashing down on a firefighter, burying him in the rubble. A frantic rescue effort was undertaken and he was located and removed from the debris.

The unidentified firefighter was rushed to San Francisco General Hospital with a leg fracture and other injuries, according to authorities. He was in stable condition.

Police Sgt. Lyn Tomioka said an illegal converter box bypassing the electrical meter was found at the site, prompting a response by the department's narcotics investigations unit.

Converter boxes are often used to try to mask crimes such as marijuana growing operations, methamphetamine labs and other illegal activities that use large amounts of energy, she said.

"But it's still undetermined whether this was a marijuana grow site," Tomioka said. "They don't know what was in that site, the place was completely engulfed and just about completely destroyed."

"The red flag is the converter box," she said.

Tomioka said the fire "is suspicious but is not considered an arson at this point."