While battling the fire, a firefighter cut his leg with a circular saw, leaving a gash six inches long and two inches deep, Alameda County fire spokeswoman Aisha Knowles said.
The cut tore into the firefighter's muscle, and he was transported to a hospital, Knowles said.
The firefighter was released from the hospital early this afternoon, she said.
Alameda County fire responded to reports of heavy smoke at the Tequila Grill taqueria restaurant at 1350 E. 14th St. near Estudillo Avenue at about 2:07 a.m., battalion chief Ron Figuera said.
The fire was upgraded from a one-alarm fire with 21 firefighters responding to a two-alarm fire with a total of 33 firefighters responding at the height of the fire, the battalion chief said.
Figuera said the fire may have started in a dumpster behind the restaurant, but the cause of the fire remains under investigation.
The fire was under control by 2:45 a.m., Figuera said.
The restaurant's owner was not immediately available for comment.