The fire was reported at approximately 2:30 a.m. Tuesday in a structure located on the 8400 block of Santa Monica Boulevard just east of La Cienega Boulevard.
Passerby Mitch Jackson told Eyewitness News that he saw the fire start and captured some of the initial flames on cellphone video. He immediately notified sheriff's deputies.
Jackson said he saw two men throw something into the building, then make a run for it when they realized they had been spotted.
"I had gone to 7-Eleven for a snack, walking past, heard glass breaking, and I looked over and there was a guy throwing what looked to be like firebombs through the window downstairs," Jackson described.
In minutes, the entire building was engulfed in flames. At the fire's peak, more than 100 firefighters were on the scene. Two were rushed to the hospital with minor injuries.
Jackson said the flames grew so intense, that he could feel the heat across the street. Fire officials said it took them about an hour to put the flames out.
"The windows were just immediately popping out. You could tell that there was something causing it to burn like that," said Jackson.
Busy Santa Monica Boulevard was shut down near La Cienega for hours. It took more than an hour to put out the flames. That's when arson and bomb squad investigators stepped in.
Jackson was asked by investigators to describe the suspects, but he said it was too dark to get a clear look at any faces.
The structure is occupied by a building management company on the first floor and a talent agency on the second floor. According to sheriff's officials, damage to the building is estimated to be around $2.5 million.
If you have any information about this fire, you're urged to contact the Los Angeles County Sheriff's Department's Arson Explosives Detail at (323) 881-7500 or LA Crime Stoppers at (800) 222-TIPS.