Thousands have been forced to flee their homes after wildfires tore through Idaho and threatened an affluent area where several Hollywood stars have properties.

On Saturday firefighters were hampered by thick smoke that shrouded the area, grounding helicopters.

"This fire is consuming everything," fire spokeswoman Madonna Lengerich told CBS. "The fire is so hot, it's just cremating even the biggest trees."

Extra officers have been deployed to help protect homes in Hailey and ski town Ketchum, and 2,300 residents have been evacuated.

1,400 residents of nearby Sun Valley were under 'pre-evacuation' orders, ready to flee if necessary.

Authorities estimate that so far only 6% of the Beaver Creek Fire has been contained, and 700 firefighters have been deployed in mountains to the west to quell the blaze.

Arnold Schwarzenegger, Bruce Willis and Tom Hanks are among the celebrities to have homes in this part of the state.

The fire is believed to have started when lightning struck dry forest on 7 August. The fire spread to cover 144 square miles by Friday, fanned by strong winds and fuelled by dry brushwood.

"It was a good day from the standpoint that we had no injuries, no lives lost, and no homes and property burned," fire spokeswoman Lucie Bond told the AP news agency on Saturday.

"Firefighters have been going house-to-house to decrease the risk. We're simply not going to leave homes unprotected."

There were also wildfires in Utah, with 10 homes in Willow Springs destroyed.

"When you get a chance to sit back and think about it, you remember all the things you didn't get out that you should have gotten out - it's too late," said Jane See, a local property owner.

The flames had not been considered a threat to communities until Friday, when strong winds pushed them over State Highway 199.

As of Saturday the Patch Springs Fire had burned 50 square miles and was 20% contained.