The fire covers more than 22,000 acres and residents of about 1,500 homes near Santa Clarita have been evacuated.
A body has been found in a burned-out car but it is not clear if the death is fire-related.
Strong winds have fanned the flames and blown smoke and ash across Los Angeles.
"It started consuming houses that were non-defendable," said Los Angeles County Deputy Fire Chief John Tripp.
He said the flames had charged through the terrain "like a freight train".