Raging wildfires threatened more homes afterthousands of residents fled towering flames fanned by high winds and record-breaking temperatures in baking southern California.On a third day of infernos which have destroyed at least 20 homes in San DiegoCounty, firefighters concentrated their efforts on hillsides in the San Marcos area,35 miles (55 kilometers) north of the city of San Diego."All available resources are being mobilized to battle this blaze. San Marcos is thetop regional priority and state-wide support has been deployed," local fire chiefs said in a statement."Mandatory evacuations in the City of San Marcos are still in place," it added, sayingthat 13,000 orders had been given and hundreds of people had taken to shelters,waiting to see if their homes would survive. An 18-unit apartment block was ravaged in nearby Carlsbad, where at least threeother homes were reported hit by the advancing flames Wednesday and Thursday. ALegoland amusement park there remained closed.Robbie Richard of the San Marcos Fire Department told AFP that recordtemperatures above 100 degrees Fahrenheit (nearly 40 degrees Celsius) and theSanta Ana winds were making it extremely challenging for his men."We are looking at temperatures that are exceeding a hundred degrees today. Thesefields are already very very dry, some of these fields haven't even burn for a decade,"he said.California and other western US states are routinely hit with wildfires during thesummer and fall, but blazes have occurred earlier in the year in recent times. Somany blazes at once in only mid-May is very rare."It is very early,"¨said Richard.On Wednesday, about a dozen non-essential staff at the San Onofre nuclear powerplant were evacuated "as a precaution" due to nearby brush fires, while crewsdoused surrounding vegetation with water as a preventive measure.A number of decades-old records for mid-May temperatures have been broken orequalled.Downtown Los Angeles sizzled in temperatures of 101 degrees Fahrenheit onThursday, tying a record dating back to 1970. At LAX international airport a readingof 97 degrees Fahrenheit was recorded, breaking the previous record of 94 degrees Fthere in 1970.