Crews battling the largest wildfire in California's history took advantage of milder overnight temperatures to gain considerable ground in containing the blaze, a day after officials said it would take until September to snuff it out.
The Mendocino Complex fire, which has scorched an area of northern California almost the size of Los Angeles, was 47 per cent contained on Wednesday morning, the California Department of Forestry and Fire Protection said, up from 34 per cent a day earlier.
So far, two firefighters have been injured fighting the blaze, which has consumed more than 121,400 hectares. While sprawling, the wildfire was less destructive than last week's Carr Fire near Redding, which burned 75 homes to the ground, forced the evacuation of more than 23,000 people and destroyed more than 1000 structures.
Overnight temperatures for Wednesday and Thursday should drop to a low of 18 degrees Celsius but highs during the day were forecast to hit 37C, said Jennifer Guenehner of the National Weather Service.
About 4000 firefighters were working to stop the fire from reaching communities at the southern tip of the Mendocino National Forest, about 161km north of San Francisco. The blaze is still threatening more than 10,000 structures, according to Cal Fire.
The Mendocino Complex is one of 17 major fires burning in California that have destroyed more than 1500 structures and displaced tens of thousands of people.
Cal Fire on Tuesday pushed back the date when it expected to bring the Mendocino fire under full control to September 1, the fourth time the department has revised its timetable as the massive wildfire expanded.
The blaze became the largest in California history on Monday, after officials began battling two separate blazes in the Mendocino area as a single event.
The blaze has surpassed last December's Thomas Fire, which scorched Santa Barbara and Ventura counties in southern California.
US Commerce Secretary Wilbur Ross on Wednesday directed federal agencies to use any water that was needed to "protect life and property" threatened by California wildfires.
In a written statement Ross said he had directed the National Marine Fisheries Service to facilitate access to the water needed to fight the fires.
On Sunday, President Donald Trump claimed, without substantiating his remarks, that California was letting water run into the ocean instead of using it to fight the flames, and blamed California's environmental policies for worsening the fires.
The comments baffled California firefighters, who said they had more than enough water to douse the flames.