More than a dozen wildfires continued to rage unstopped in southern California for a third day today , forcing an estimated 300,000 people to evacuate their homes and blackening over 400 square miles of brushland and suburbs.

Hot, gusting winds made the advancing flames nearly impossible for firefighters to control, officials said. The winds are expected to keep blowing through the day, and perhaps longer.

The worst conditions continued to be in San Diego County, where large sections were under mandatory evacuation orders. Several hundred houses appeared to have been destroyed or heavily damaged, according to the governor’s Office of Emergency Services, and thousands more were in danger.

Officials appealed to residents outside the evacuated areas to stay at home if possible and to limit their use of cellular phones, to keep highways and communication lines clear for emergency use.

Governor Arnold Schwarzenegger said 800 National Guard troops would be diverted from duty on the southern border to assist with evacuation and ground control in the county. The fires, a Hydra with at least 15 separate burns in seven counties fed by gale-force winds, burned some 267,000 acres from Santa Barbara to the Mexican border. Engines and firefighters from as far as Nevada and Arizona were summoned as resources were stretched to the limit.