LOS ANGELES—A search of a two-story downtown commercial building that housed an illegal cannabis operation revealed no indication that anyone was killed during a blaze Saturday morning.

Five firefighters were hospitalized for comprehensive medical examinations after experiencing an unexpected burning sensation to their faces, according to the Los Angeles Fire Department’s Brian Humphrey. Those firefighters were treated and released from medical care. No other civilian or firefighter injuries were reported.

The fire broke out around 8 a.m. Saturday at a 69-year-old, 9,100-square-foot brick structure at 1400 E. Newton Street, a couple of blocks north of the Santa Monica (10) Freeway, sending a huge plume of smoke into the air that was visible for miles.

Some 145 firefighters knocked down the blaze in 56 minutes, Mr. Humphrey said.

A pair of cadaver-detection dog teams were called to the scene “to address unconfirmed reports that one or more persons may have been within the now-heavily damaged building at the time of the fire,” he said. They found no indication of human remains and no witnesses came forward to report anyone missing.

The cause of the fire was under investigation.