Oct. 13 (UPI) -- Multiple wildfires burning in California have merged and three were fully contained Friday as officials put the death toll in the northern portion of the state at 33.
Cal Fire, the state's fire agency, said firefighters were battling 17 fires across the state, down from nearly two dozen.
"Several of the wildfires merged with other fires, while full containment was made on three others," the agency said.
Cal Fire Director Ken Pimlott said the wildfires, strengthened by high winds, continue to burn and "have the potential to shift in any direction at any time."
A statewide summary Friday afternoon said more than 220,000 acres have burned since the fires started last weekend. More than 8,000 firefighters, many from other states, were trying to extinguish flames across the region's wine country.
More than 3,500 homes and other structures have been destroyed in the area -- nearly 3,000 homes and 400,000 square feet of commercial space in Santa Rosa alone. Mayor Chris Coursey said he expects those figures to increase, and noted that the city's new firehouse was leveled.
Officials said at least 17 people have died in Sonoma County, nine in Mendocino County, four in Yuba County and two in Napa County. Sonoma County officials listed more than 1,100 missing persons. Although about 600 were located, about 400 remain missing, Sheriff Rob Giordano said on Thursday.
The wildfires are among the deadliest in California's history.
Officials said 64 of 77 cellphone towers in the area have been damaged, but repaired.
The National Weather Service issued red flag warnings for the East Bay hills and North Bay mountains, which indicate high fire danger. NWS meteorologist Rick Canepa said winds are expect to increase to 20 to 30 mph -- with gusts up to 60 mph -- on Friday and Saturday, conditions that are expected to make fighting the flames even more difficult.
The smoky air, which has penetrated San Francisco and San Jose, is not expected to improve though the weekend, either. Air quality was rated as "unhealthy" in most of the Bay Area and "unhealthy for sensitives groups" farther south, said Kristine Roselius of the Bay Area Air Quality Management District.
Schools and businesses closed throughout the area, and numerous events scheduled for the weekend were canceled.
As of Friday afternoon:
-- The Tubbs Fire in Sonoma and Napa counties burned 34,770 acres and was 25 percent contained.
-- The Pocket Fire in Sonoma County burned 9,996 acres and was 5 percent contained.
-- The Nuns Fire in Sonoma County burned 44,381 acres and was 5 percent contained.
-- The Pressley Fire in Sonoma County burned 473 acres and was 10 percent contained.
-- The Atlas Fire in Solano and Napa counties burned 48,228 acres and was 27 percent contained.
-- The Patrick Fire in Napa County burned 12,379 acres and was 18 percent contained.
-- The Redwood/Potter fires in Mendocino County burned 34,000 acres and was 10 percent contained.
-- The Sulpher Fire in Lake County burned 2,500 acres and was 55 percent contained.
-- The Cascade Fire in Yuba County burned 10,120 acres and was 55 percent contained.
-- The Lobo Fire in Nevada County burned 829 acres and was 52 percent contained.
-- The McCourtney Fire in Nevada County burned 76 acres and was 89 percent contained.
-- The LaPorte Fire in Butte County burned 6,139 acres and was 45 percent contained.
-- The Cherokee Fire in Butte County burned 8,417 acres and was 70 percent contained.
-- The Honey Fire in Butte County burned 150 acres and was 75 percent contained.
-- The Silver Fire in Fresno County burned 58 acres and was 80 percent contained.
-- The Quarry Fire in Kern County (183 acres), Point Fire in Calaveras County (130 acres) and 37 Fire on Sonoma County (1,660 acres) were 100 percent contained.