California's Governor Jerry Brown has declared a state of emergency for Los Angeles as the city faces its largest ever wildfire.

The move frees up state resources to battle the blaze, which has scored some 2,400 hectares north of central Los Angeles in the Verdugo Mountains.

The blaze has prompted the closure of a major highway and is only 10 percent contained.

More than a thousand firefighters are battling the slow moving La Tuna blaze, and officials warn it could become erratic if winds kick up amid soaring temperatures.

Seven hundred homes have been evacuated.