The August Complex Fire, which became California's largest-ever wildfire this week, has merged with several other blazes and grew to 746,607 acres, up from 471,185 a day earlier, authorities said.
In a statement on Friday, the California Department of Forestry and Fire Protection (Cal Fire) said the blaze was 25 per cent contained, reports Xinhua news agency.
According to Cal Fire, five of the 20 largest fires in California's history are currently raging across the state.
The SCU and LNU lightning complex fires, largely contained in the San Francisco Bay Area, are the third and fourth largest, respectively.
Two other ongoing blazes in the top 20 are the North Complex, which has been burning since August 18 in Plumas County, at the ninth position, and the Creek Fire in Fresno and Madera counties at number 16.
Twenty-nine major wildfires were still burning across California as of Friday, with approximately 14,000 firefighters battling them, Cal Fire reported.
The National Park Service announced the closure of Muir Woods, Alcatraz and Fort Point in the San Francisco Bay Area due to unhealthy air quality throughout the region.
The executive director of San Francisco's Department of Emergency Management, Mary Ellen Carroll, advised residents Friday that with smoke making the air unhealthy to breathe, people should stay inside with doors and windows closed.
"If you are able to stay home, we encourage you to stay home," she was quoted as saying in a San Francisco Chronicle report.
The state's death toll has also continued to rise.
Authorities in Butte County, north of the capital Sacramento, said 10 bodies have been found in the last two days, while another 16 people are reported as missing.
The overall death toll in California currently stood at 20 since August 15, when the first series of blazes began.
