Firefighters faced more dry, windy conditions on Friday that could whip up wildfires in Northern California that have killed at least 31 people and left hundreds missing in the heart of wine country.
The most lethal wildfires in California's history have killed people while they slept in their beds and prompted authorities to order thousands of residents from their homes, warning anyone deciding to stay: "You are on your own."
The toll from the more than 20 fires raging across eight counties could climb, with more than 400 people in Sonoma County alone still listed as missing.
Winds of up to 60 mph (100 kph) and humidity of just 10 percent will create "critical fire weather conditions" and "contribute to extreme fire behavior" on Friday afternoon and into Saturday, the National Weather Service said.
A force of 8,000 firefighters was working to reinforce and extend buffer lines across the region where the flames have scorched more than 190,000 acres (77,000 hectares), an area nearly the size of New York City.
With 3,500 homes and businesses incinerated, the so-called North Bay fires have reduced entire neighborhoods in the city of Santa Rosa to smoldering ruins dotted with charred trees and burned-out cars.
The cause was under investigation, but officials said power lines toppled by gale-force winds on Sunday may be to blame.
The Napa Valley town of Calistoga faced one of the biggest threats, and its 5,000-plus residents were ordered to leave their homes as winds picked up and fire crept closer.
Calistoga Mayor Chris Canning said anyone refusing to heed the mandatory evacuation would be left to fend for themselves if fire approached, warning on Thursday: "You are on your own."
Sonoma County accounted for 17 of the North Bay fatalities, all from the Tubbs fire, which now ranks as California's deadliest single wildfire since 2003.
Some people killed were asleep when flames engulfed their homes, fire officials said. Others had only minutes to escape as winds fanned fast-moving blazes.
Mark Ghilarducci, state director of emergency services, said the loss of cell towers likely contributed to difficulties in warning residents.
As many as 900 missing-person reports have been filed in Sonoma County and 437 people have since turned up safe. It remains unclear how many of the 463 still unaccounted for are fire victims rather than evacuees who failed to alert authorities, Ghilarducci said.
From the Vatican, Pope Francis issued a statement expressing his "heartfelt solidarity" with all those affected.
"He is especially mindful of those who mourn the loss of their loved ones and who fear for the lives of those still missing," the statement said.
The fires struck the heart of California's world-renowned wine-producing region, wreaking havoc on its tourist industry and damaging or destroying at least 13 Napa Valley wineries.
The state's newly legalized marijuana industry was also hit hard, with at least 20 pot farms in Sonoma, Mendocino and Napa counties ravaged, a growers' association said.