Benicia fire crews arrived at the fire near Interstate Highway 780 at the E. Fifth Street on-ramp around 3:30 p.m., Benicia Fire Marshal Ray Iverson said.
By 4 p.m. the fire was contained and no injuries had been reported, he said.
Nearby buildings, including single-family homes, were damaged by the fire that spread across two acres, but the full extent of the damage is not yet known, Iverson said.
The cause of the fire has yet to be determined, he said.
California Highway Patrol Officer Eric Anderson said the fire did not jump onto the freeway after it was reported at 3:12 p.m. near the freeway on-ramp.
Oakland resident Kyle Hixson was on the other side of the Carquinez Strait in Port Costa looking toward Benicia when he saw a plume of smoke and flames erupt around 3 p.m.
"I saw smoke piling up and I saw flames from across the bay," he said about the fire that was smoldering and contained by 4 p.m.