Media playback is unsupported on your device Media caption The fires are being blamed on high temperatures and years of drought, as James Cook reports

The governor of California has declared a state of emergency after wildfires forced about 23,000 people to flee their homes in the north of the state.

Governor Jerry Brown said the fires, which have left one person dead, destroyed and threatened buildings in the Napa and Lake counties.

More than 1,300 people fled Middletown, north of San Francisco, as their homes were consumed by the flames.

Four firefighters who were badly burned are receiving treatment in hospital.

Wildfires were still burning on Monday after devastating homes and apartment blocks over the weekend.

The woman who died was a disabled 72-year-old retired teacher, Barbara McWilliams, who lived on her own in Lake County on Cobb Mountain.

Her carer, Jennifer Hittson, told the local media she had advanced multiple sclerosis that meant she was unable to walk unaided.

Ms Hittson said she had asked the authorities to help her but by the time they got there, her home was already engulfed in flames.

At the scene - James Cook, BBC News, Middletown

You can smell the so-called Valley Fire before you see it. An acrid stench hangs in the air on the road to Middletown. Smoke is thick in the sky, smothering the pines and the dry brush on the hillsides.

But it does not prepare you for the devastation in the little town itself. Home after home lies in ruins. Families who have lost everything have returned to pick through the debris but there doesn't appear to be anything to salvage.

Some houses have survived with scorch marks. Others are unscathed. But everyone here is stunned by the speed and ferocity of the fire which swept through in minutes, whipped up by a harsh, dry wind.

In the heart of this tight-knit community, a twisted mass of metal and ashes was, we are told, an apartment block of nearly 50 homes. The people of Middletown say they will rebuild. That will not be easy.

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Image copyright AP Image caption A mother is consoled by her daughter at their destroyed home in Middletown

Image copyright AP Image caption Fire damaged trees were removed

Up to 1,000 structures, which includes barns and sheds, have been burned, fire agency spokesman Daniel Berlant said.

The fires across northern California are being blamed on high temperatures and years of drought.

The state spent $212m (£137m) fighting the flames in July alone, California's forestry and fire protection department spokesman Daniel Berlant told the AFP news agency.

He said more than 275 homes and other buildings had been destroyed and the Red Cross is opening emergency shelters for evacuated residents.

Image copyright AFP Image caption Firefighters have been tackling some of the blazes for about a week

Image copyright Reuters Image caption The fire left burned out vehicles and homes in its wake, seen here in Middletown, California

One blaze, the Valley Fire, which started on Saturday in Lake County, is said to have burned 40,000 acres (16,190 hectares).

It reached the centre of the small town of Middletown on Sunday. Its 1,500 residents had already been ordered to evacuate.

The fire spread quickly and witnesses saw flames reach up to 200ft (60m) in the air, according to local news reports.

Further east, in Amador and Calaveras counties, around 4,000 firefighters were battling the Butte Fire, which broke out on Wednesday.

That blaze has so far destroyed around 65,000 acres (26,300 hectares) along with 86 homes and 51 outbuildings. It is only 15% contained and threatens more than 6,000 other buildings, officials say.

Further south, beyond Fresno, firefighters have been tackling the largest of the blazes, the so-called Rough Fire, which has claimed 128,800 acres (52,000 hectares) since it began in late July.

Nearly 3,000 firefighters are tackling that blaze, which is now said to be 29% contained.

They have evacuated the Kings Canyon National Park and working to protect the park's famous grove of Giant Sequoia trees.