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.