A firefighting plane has crashed in northern California, killing all three crew members, while wildfires continue to rage across several areas of the United States.

The air tanker, which was being used to fight a blaze near Yosemite National Park, caught fire and crashed in the town of Walker, just missing a mechanic's shop, witnesses said.

Amateur video shots by a passer-by showed that both wings fell off the plane in mid-air, before it spiralled down to the ground and exploded in a ball of flame.

There are now 20 large fires in 11 states

There was no immediate word on why the aircraft had come apart.

In a separate incident in southern California, three firefighters were injured in fires east of Los Angeles, which also blocked the interstate route to Las Vegas, said Karen Terrill, spokeswoman for the state forestry agency.

In all, 20 large fires were burning in 11 states across the country on Monday.

Thousands of acres of forest are lost to wildfires each summer in the western US, due to a combination of drought and high winds increasing the risk of fire.

This year - one of the driest in decades - the fires began earlier than usual.

The state of Colorado is the worst hit. It is now battling its largest wildfire ever, which has scorched some 40,000 hectares (99,000 acres) of land and forced 5,400 people to leave their homes.

Forest worker charged

A US federal magistrate has ordered a fire prevention officer to be held without bail on charges of starting one of the Colorado wildfires.

The cost of fighting the blazes is estimated at $20m

Forestry technician Terry Barton, 38, attended a court hearing on Monday, accused of setting fire to timber in a national forest, damaging government property, and making false statements to investigators.

Ms Barton has already admitted starting a blaze while patrolling the Hayman area of Pike National Forest to enforce a fire ban, according to US federal prosecutor Bill Leone.

She said she had decided to burn a letter from her estranged husband which had upset her.

She set fire to it in an authorised camp fire site and then left believing she had extinguished the fire, she said.

But driving past the site after turning round her vehicle she found that the fire had spread beyond the camp fire ring. She tried but was unable to suppress the fire.

If convicted, Ms Barton could be sentenced up to 10 years in prison and fined up to $250,000.