Photo: The Canadian Press

Teams with cadaver dogs began a grim search Thursday for more dead in parts of California wine country devastated by wildfires, resorting in some cases to serial numbers stamped on medical implants to identify remains that turned up in the charred ruins.

Many of the flames still burned out of control in fires that spanned more than 300 square miles (777 square kilometres), an area equivalent to the size of New York City's five boroughs.

Sonoma and Napa counties endured a fourth day of choking smoke while many residents fled to shelters or camped out on beaches to await word on their homes and loved ones.

A forecast for gusty winds and dry air threatened to fan the fires, which claimed their 29th victim and are fast becoming the deadliest and most destructive in California history.

Some of the state's most historic tourist sites, including Sonoma city and Calistoga in Napa Valley, were ghost towns as firefighters tried to stop the advancing infernos.

Calistoga, known for wine tastings and hot springs, was deserted Thursday except for dozens of firefighters staged at street corners as ash rained down on them and a thick haze covered the ground. Mayor Chris Canning warned that fires were drawing closer and all of the city's 5,000 residents needed to heed an evacuation order.

"This is a mandatory evacuation. Your presence in Calistoga is not welcome if you are not a first responder," Canning said during a news briefing, explaining that firefighters needed to focus on the blazes and had no time to save people.

A few residents left behind cookies for fire crews with signs reading, "Please save our home!"

Sonoma County Sheriff Robert Giordano said officials were still investigating hundreds of reports of missing people and that recovery teams would begin conducting "targeted searches" for specific residents at their last known addresses.

"We have found bodies almost completely intact, and we have found bodies that were nothing more than ash and bones," the sheriff said.