California Rim Fire is 'one fifth contained'

Firefighters are slowly making progress against a sprawling wildfire that is now 20% contained in and around California's Yosemite National Park.

But the Rim Fire has continued to spread and now spans more than 250 sq miles (650 sq km), officials say.

The flames are raining ash on a key reservoir that supplies water and hydro-electric power to San Francisco.

City officials say they are moving water to lower reservoirs and monitoring supplies for contamination.

The blaze is also threatening thousands of homes and some of California's renowned giant sequoia trees.

Some 3,680 firefighters are tackling the flames in difficult terrain.

Fanned by strong winds, the fire is burning at the edge of the Hetch Hetchy reservoir, which supplies San Francisco with 85% of its water.

Visibility in the smoke-ridden area is down to 100ft (30m), but ash reportedly falling on the reservoir like snow has not yet reached the water intake valves.

"It looks great out there. No concerns," Glen Stratton, an operations chief on the fire suppression team, said on Monday evening.

Harlan Kelly Jr, general manager of the city's Public Utilities Commission, said as much water as possible had been brought down from the reservoir and local storage had been replenished.

The blaze has become so large that it was reportedly creating its own weather patterns.

Karen Nyberg, a US astronaut based at the International Space Station,tweeted a satellite picture of the Rim Fire's giant smoke plumes.

The blaze began on 17 August in the Stanislaus National Forest from a still unknown cause.

Evacuations, some voluntary and some mandatory, are taking place. Despite the threat to some 5,000 homes, only a few have been destroyed.

California Governor Jerry Brown has declared a state of emergency for San Francisco 150 miles (220km) away as the blaze is also threatening power lines that bring electricity to the city.