Crews are struggling with hot, dry conditions as they work to get the upper hand on a massive wildfire in Southern California that has rained ash on downtown Los Angeles.

The four-day-old blaze is fanning out in all directions and threatening some 12,000 homes. Thousands have been forced to flee and Gov. Arnold Schwarzenegger is urging those in the fire's path to listen to authorities and evacuate.

Three people have been burned by the flames, including two who tried to ride out the firestorm in their backyard hot tub. Police say they "completely underestimated the fire."

Some 2,000 firefighters are trying to beat back the blaze, which is just 5 percent contained.

Three homes are confirmed destroyed and officials say they expect that number to rise.