(Updates with increased acreage burned, and 20 percent containment)

LOS ANGELES, Oct 4 (Reuters) - A wildfire fanned by erratic winds chased thousands of people from their homes in a mountaintop town 80 miles (130 km) east of Los Angeles, officials said on Sunday.

The so-called Sheep Fire, which has charred 7,500 acres (3000 hectares) since Saturday, reached the outskirts of Wrightwood, a bucolic resort in the San Gabriel Mountains with a population of about 4,000.

It destroyed at least three isolated houses, but officials said they were confident they could save Wrightwood. By late Sunday, the fire was 20 percent contained, and they hoped that cooler weather would help them make progress overnight as wind speeds dropped.

The cause of the fire was unknown.

Authorities issued a mandatory evacuation order for Wrightwood earlier in the day as unpredictable winds gusted up to 50 miles (80 km) an hour.

More than 1,000 firefighters battled the flames, waging aerial assults when winds permitted and setting backfires.

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