The cause of the blast was not known.
The hydraulic fluid, called therminol, is used in the heat-transfer process in generating solar power. The plant is owned by Sun Ray Energy.
Correspondent Sophia Choi of CBS station KCBS-TV in Los Angeles reports that people living 15 miles away from the plant felt the explosion, and commercial pilots flying 40 miles away could see it.
Brian Rodriguez, who lives in nearby Barstow, said the explosion sent glowing, pulsating clouds into the sky. "Man, it was pretty neat," he added.
Because the fluid in the tank is not toxic, firefighters say they are just letting the fire burn itself out, which probably will happen sometime during the day Saturday.