US firefighters in California have reported progress as they battle a wildfire near Yosemite National Park for a 10th day.
Almost 3700 firefighters, dwarfed by towering flames that lit up the night sky in California, have been battling the blaze.
Although ash from the fire reached the reservoir that supplies San Francisco's drinking water, crews said on Tuesday they were confident the reservoir's infrastructure could be protected, local news reports said.
The so-called Rim Fire, the 13th largest in state history that closed the road into one of the country's top tourist destinations, is now 20 per cent contained, the Los Angeles Times reported, quoting Yosemite Fire Chief Kelly Martin. That was up from 7 per cent on Sunday.
The blaze has charred nearly 65,000 hectares - including about 8,500 hectares inside the park - and destroyed at least 23 structures, the California Department of Forestry and Fire Protection said.
The fire is also threatening two groves of giant sequoias and historical structures in the park.
The Hetch Hetchy Reservoir, the main source of fresh water for 2.6 million people living in the San Francisco Bay Area, is about 320 kilometres to the west.
Schools in several nearby areas remained closed on Monday.
Meanwhile, the park said in an update on its website, "most of Yosemite National Park is not affected by the fire and is relatively smoke-free. The northern part of the park ... has some smoke. Conditions may change if winds shift."
Highway 120, one of the main routes into Yosemite from the west, remained closed.
Governor Jerry Brown has declared a state of emergency for San Francisco because of the threat to its water and electricity.
The state's firefighting efforts got a boost when California received federal assistance over the weekend to help mobilise the necessary resources.
President Barack Obama spoke to California's governor on Sunday and "expressed his gratitude for the brave men and women working tirelessly to combat this devastating fire", the White House said.
"The president reiterated his commitment to providing needed federal resources to support the ongoing state and local response," it added in a read-out of the call.
