TEAMS with dogs have begun a grim search for more dead in parts of California wine country devastated by wildfires.

Searchers resorted in some cases to using serial numbers stamped on medical implants to identify remains that turned up in the charred ruins.

New deaths confirmed on Thursday took the toll to 31, making it the deadliest week of wildfires in California history.

Many of the flames still burned out of control, and the fires grew to more than 300 square miles, an area as large as New York City.

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 further.

Some of the state’s most historic tourist sites, including Sonoma city and Calistoga in Napa Valley, were ghost towns populated only by fire crews trying to stop the advancing infernos.

Calistoga mayor Chris Canning warned that the fires were drawing closer and all of the city’s 5000 residents needed to heed an evacuation order.

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”.