Media playback is unsupported on your device Media caption California districts wiped out by wildfires

California officials have ordered an entire town to evacuate as "conditions have worsened" in wildfires that have now killed 26 people.

All residents of Calistoga were directed to leave the area on Wednesday night, Napa County officials said.

About 60 prison inmates have joined hard-pressed firefighters in battling the fast-moving blazes, the state fire chief says.

Among the areas scorched by the 22 blazes are marijuana farms.

'Explosive vegetation'

On Thursday morning, Sonoma County Sheriff Rob Giordano said 463 people are still unaccounted for.

Nine hundred people have been reported missing since the fire started on Sunday night, but a large number have been located, he added.

The night before, all 5,000 residents of Calistoga, in Napa County, were told to leave as police blocked traffic from approaching the area.

Geyserville, a town of around 800 people, and the community of Boyes Hot Springs, both in Sonoma, were also evacuated.

"It's going to continue to get worse before it gets better," state fire Chief Ken Pimlott said.

He warned that the death toll could rise further.

"We are still impacted by five years of drought," he added.

"These fires were driven by the critically dry fuel bed. We are literally looking at explosive vegetation."

The wildfires, fanned by 50mph (80km/h) wind gusts, have razed more than 3,500 buildings and homes spanning 170,000 acres (68,800 hectares).

Interactive Slide the button to see how a Santa Rosa community was devastated After Before

Renewed high winds are fanning the "catastrophic" blazes, said state fire officials, which were spreading unpredictably in their fourth day.

Firefighters are going door to door in the state's wine-producing region, evacuating those left behind ahead of the next wave of blazes.

Some homeowners complained that the flames had reached their doors ahead of any official warnings.

Many residents did not receive notifications on their mobile phones, similar to the Amber Alert issued for missing children.

Sheriff Giordano said Sonoma County uses a system that requires sign-up to receive such messages.

Image copyright Getty Images Image caption The fires are spreading

The wildfires have damaged or demolished at least 13 Napa Valley wineries, a vintners' trade group says.

Cannabis plantations in fire-scorched Mendocino County could lose millions as many are uninsured, according to Nikki Lastreto of the local industry association.

Marijuana farmers cannot insure their businesses since federal law bans the drug.

Though recreational cannabis was legalised in the state in 2016, California's retail market does not open until next January.

Image copyright AFP/Getty Image caption Entire neighbourhoods in the town of Santa Rosa have been destroyed

This means some farmers who have invested millions may be left without a business once the smoke clears.

The fires are among the deadliest in California's history and have sent smoke as far south as San Francisco, about 50 miles away.

More than 200 fire engines and crews are being rushed to California from the rest of the US, officials said.

Mr Pimlott said 73 helicopters, 30 air tankers and nearly 8,000 firefighters were currently battling the blazes.

Media playback is unsupported on your device Media caption Fire survivor: 'I don't have any neighbours any more.'

The conflagration has reduced entire neighbourhoods in the city of Santa Rosa, a city of 175,000 people, to ash.

Fourteen of the deaths have occurred in Sonoma County, officials say.

Some 25,000 people across the county have been evacuated and 40,000 homes are without power.

Six people have died in Mendocino County, four in Yuba County and two in Napa County, officials said.