Some sequoias are up to ten metres wide at their base

They are using water-carrying aircraft and helicopters to prevent the flames reaching the centuries-old trees in the Giant Sequoia National Monument, north of Los Angeles.

A 45-year-old woman who was cooking hotdogs when her campfire blew out of control is thought to be to blame for the blaze.

She was arrested at her home as flames rapidly devoured the tinder-dry brush, their progress fuelled by erratic winds.

Two hundred more people have now been evacuated from their homes in addition to the 1,000 who have already been forced to flee.

No rain

The wildfire is now just a couple of kilometres from the Sequoias, some of which are more than a 100 metres high and 10-metres wide.

Known as the Trail of 100 Giants, the trees are part of an area that has been declared a national monument.

The fire has already burned through nearly 20,000 hectares (50,000 acres), about half of it in the Sequoia National Forest, 200 (124 miles) kilometres north of Los Angeles.

"More than 100 giants between 300 and 1,300 years old are threatened, and hundreds of other smaller sequoias are in danger as well," said Jennifer Combs, spokeswoman for the US Forest Service who described the trees as "priceless".

The fight has been hampered by high winds and the dry conditions. The area has not seen rain since spring.

The fire is still far from the giant sequoias located inside the smaller Sequoia National Park, and was not thought to be a threat to the 83.8-metre (275-foot) General Sherman Tree - a tourist attraction believed to be the world's largest tree by volume.

Fires have ripped through several parts of the US and Canada in recent months.

Firefighters in Colorado battling a blaze near Rocky Mountain National Park believe the 1,760-hectare (4,400 acre) blaze will be contained by Saturday, and crews from the area have been sent elsewhere.