Yosemite boundary burns in California Rim FireThe fire is 7% contained, officials say
Firefighters in California are struggling to gain control of a huge wildfire which has reached the edge of Yosemite National Park.
Known as the Rim Fire, it covers an area of nearly 203 sq miles (526 sq km) and threatens a major reservoir serving San Francisco.
More than 5,000 homes are endangered by the blaze, which began on 17 August in the Stanislaus National Forest.
The fire is now 7% contained, officials say, up from 2% on Friday.
More than 2,700 firefighters are tackling the flames in difficult terrain.
A spokesman for the California Department of Forestry and Fire Protection, Daniel Berlant, said the fire was the 16th-largest on record in California.
"We are making progress but unfortunately the steep terrain definitely has posed a major challenge," he said.
Evacuations, some voluntary and some mandatory, are taking place. Despite the threat to thousands of homes, only a few have been destroyed.Tourist area
California Governor Jerry Brown has declared a state of emergency for San Francisco 150 miles (220km) away as the blaze is threatening power lines that bring electricity to the city.
The city's water supplies could be affected if the blaze reaches Hetch Hetchy reservoir, which supplies San Francisco with 85% of its water. The fire is burning some four miles away from the reservoir which serves some 2.6 million customers.
Two of three hydroelectric power stations serving the city were shut down.
The blaze, which continued for a week on the edges of Yosemite, reached the park's backcountry at Lake Eleanor on Friday. But it remains some 20 miles away from Yosemite's main tourist area.Continue reading the main story
The park authorities say they have no plans to close as most of Yosemite, which hosts up to 15,000 visitors a day in the summer, is unaffected by the fire.
Areas on the north-western edge of the park, including that round the Hetch Hetchy reservoir and Lake Eleanor, have been closed throughout the week.
A stretch of motorway, Highway 120, which is one of three entrances to the west side of the park, remains closed. Visitors are being urged to use alternative routes from the west.
The "Rim" fire is one of 50 major wildfires burning in the western US. Lack of rain and snow have made it a bad year, with 5,700 fires being tackled so far.
The "Beaver Creek" fire in Idaho has destroyed some 45,000 hectares near the ski resort of Sun Valley.
Meanwhile, five wildfires in Yellowstone National Park have scorched about 18 square miles of mostly remote areas.