Yosemite fire shuts new road before US holiday weekend

US authorities closed a second main road into the Yosemite Valley tourist landmark Wednesday as over 4,000 firefighters battled to stop a huge blaze spreading further into the national park, AFP reports. The decision came days before America's Labor Day weekend, when a surge of visitors is typically expected at California's Yosemite National Park, which draws millions of tourists every year. As well as clouding the tourist spot, the so-called Rim Fire is also threatening to contaminate San Francisco's water supply, as it drops a rain of ash onto a key reservoir feeding the West Coast city. Last week officials closed Highway 120, the main road used by visitors from San Fransisco into the west of the park. There are three other main roads in: another from the west, one from the south, and one from the east. From noon (1900 GMT) Wednesday authorities closed a key section of the Tioga Road, which runs horizontally across the park, effectively blocking access from the east into Yosemite Valley, the spectacular area at its heart. The road will likely remain closed through the Labor Day weekend to allow crews to carry out fire suppression activities in the area, said park Superintendent Don Neubacher. The so-called Rim Fire -- California's seventh biggest ever -- now covers some 293 square miles (760 square kilometers), an area bigger than Chicago, according to the California Department of Forestry and Fire Protection (Cal Fire). "Rapid fire growth and extreme fire behavior continue to hamper suppression efforts," firefighters warned in the latest update on the Inciweb multi-agency website. The blaze, which broke out August 17, is now 23 percent contained, compared to 20 percent on Tuesday, it said. A total of 4,191 firefighters are now involved in battling it. On the eastern edge of the blaze, flames are racing unimpeded because the terrain is relatively flat. "They're in scouting mode," Dick Fleishman of the US Forest Service told the Los Angeles Times, referring to fire crews. "There's not a lot of real good areas to get out in there and do a lot of work." The blaze has forced the closure of multiple campgrounds and other facilities in the area, and has also threatened a number of groves of giant sequoia trees, some of the world's biggest and oldest living organisms. But it remains more than 15 miles away from the majestic Yosemite Valley, visited by millions of tourists every year to see natural wonders including the Half Dome and El Capitan rock formations. Ash from the inferno has however reached the reservoir that supplies San Francisco's drinking water. The Hetch Hetchy Reservoir is the main source of fresh water for 2.6 million people living in the San Francisco Bay Area, some 200 miles (320 kilometers) to the west. No injuries or deaths have been reported due to the blaze, but it has destroyed at least 111 structures -- 31 homes as well as buildings on camp grounds that were hastily evacuated last week when the fire erupted. More than 5,500 buildings, including 4,500 homes, remain under threat, according to Cal Fire. The fire's potential to grow and the difficulty of the terrain were both still described as "extreme" by the Inciweb update. But the park stressed again Wednesday that "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."