MARIPOSA, California - A wildfire that has forced thousands of Californians to flee their homes exploded in size on Wednesday, threatening a picturesque gold rush town outside Yosemite National Park as dozens of blazes scorched the west of the United States.

More than 2,200 firefighters have contained just 7 percent of the Detwiler Fire, which is approaching the town of Mariposa and tiny communities in the foothills of the Sierra Nevada mountains, the Cal Fire state agency said on its website.

The blaze has mushroomed to 19,400 hectares, an increase of about 9,300 hectares compared with the day before. The fire has destroyed 29 structures and is threatening some 1,500 more structures, local media reported.

Firefighters are facing "extreme and aggressive fire behavior" with solid walls of flame and sparks from the main blaze setting spot fires in grasslands, the California Department of Forestry and Fire Protection said.

Flames have destroyed eight structures southwest of Yosemite National Park and the fire is threatening power lines to the park, but no one has been injured, it said.

The fire has forced more than 4,000 people from homes in and around a halfdozen small communities, officials said.

Heavy smoke hung in the air over Mariposa, a town of 2,000 with century-old wooden buildings, including what's touted as the oldest active courthouse west of the Rocky Mountains.

Tony Munoz, 63, and his wife, Edna Munoz, 59, were ordered out of their home outside Mariposa on Tuesday. They grabbed clothes, medicine and their three dogs and a cat and fled.

Driving out on narrow roads clogged by others getting out "you couldn't even see the sun" in the ash-filled sky, said Tony Munoz, a school custodian.

Reuters - Ap - Xinhua