LOS ANGELES—Ferocious desert winds pushed one of three major wildfires burning across Southern California to nearly double its size overnight, firefighters said Tuesday, the third day of the blazes that have destroyed dozens of homes and forced thousands to flee. One person was killed by the flames; another died in a car crash as a blaze neared the freeway.

The fires have charred more than 25 square miles in suburban Los Angeles and northern San Diego County, with the fiercest blazes burning in the San Fernando Valley, about 30 miles northwest of Los Angeles. Investigators are looking into the cause of all three fires.