Crews report progress fighting US wildfire

A fire truck passes burning trees as firefighters continue to battle the Rim Fire near Yosemite National Park.

TUOLUMNE CITY, UNITED STATES // Crews were finally making progress against a massive US wildfire burning near Yosemite National Park as the fire entered its 10th day yesterday.

Although ash from the fire reached the reservoir that supplies San Francisco's drinking water, crews said they were confident the reservoir's infrastructure could be protected.

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 161,000 acres, including about 21,000 acres inside the park and destroyed at least 23 structures, the California Department of Forestry and Fire Protection said.

Crews dropped flame retardants on vulnerable areas.

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 320 kilometres to the west.

The fire is being tackled by nearly 3,700 firefighters. Schools in several nearby areas remained closed.

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. The California 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.

The president, Barack Obama, spoke to Mr Brown 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 said.

The US forest service said the fire was threatening about 4,500 structures.

Heavy smoke settling low to the ground could limit visibility, but higher humidity was expected yesterday, which could help dampen the flames, said Matt Mehle, a National Weather Service meteorologist assigned to the fire.

California fire spokesman Daniel Berlant said crews were anticipating cooler temperatures and higher humidity this week that could allow them to gain control of the fire.

Rugged terrain, strong winds and dry conditions have hurt firefighters' efforts to contain the fire. The cause has not been determined.

* Associated Press with additional reporting by Agence France-Presse