The fire was reported shortly after 4 a.m. by a police sergeant who smelled smoke in the area of Grant Avenue Cafe, located at 1433 Grant Ave., district spokeswoman Sandy Wargo said.
While battling the flames, firefighters noticed the temperature in the building beginning to rise and exited the building about 40 seconds before a loud explosion rocked the cafe, Wargo said.
The explosion was the result of a flashover, a combustion caused by heat buildup inside a confined space, Wargo said.
The incident commander captured footage of the explosion, which Wargo said would be posted on the district's Web site at www.novatofire.org later today.
Firefighters had the fire under control by 4:40 a.m. No injuries were reported, Wargo said.
The cause of the fire is under investigation, although it appeared to have started near the back of the cafe, Wargo said.
She said the cafe did not have a sprinkler or alarm system. If it did, she said, "people might have been eating lunch there this afternoon."
There is no estimate yet on the cost of the damage, but Wargo said it was mostly confined to the cafe. Russeau's Fine Art Framing, a business next to the cafe, sustained minimal smoke and water damage, she said.