SAN FRANCISCO, California - The wildfire threatening Yosemite National Park is spreading further into the US tourist landmark, officials said Thursday as they battled to stop it clouding a holiday weekend.
Efforts to contain the so-called Rim Fire, which has grown to become California's sixth biggest wildfire ever, were also being boosted by the deployment of a military drone approved by the Pentagon.
The fire, which now covers more than 192,000 acres, or 300 square miles, and is 30 per cent contained, has also threatened San Francisco's water supply, due to ash falling on a key reservoir.
The blaze, about a quarter of which is now inside the park's boundaries, "is expected to continue its eastward spread farther into the west side of Yosemite National Park," said the latest firefighters' online update.
The fire, which started west of the park on August 17, is threatening some 4,500 structures and on Wednesday forced the closure of a second main road into the major US tourist attraction ahead of the Labor Day weekend.
A surge of visitors is typically expected over this weekend's Labor Day holiday at Yosemite, which draws millions of tourists every year, most in July and August. Labor Day traditionally marks the end of the summer season.
"On a normal holiday weekend we see anywhere between 15,000-21,000 people ... I still expect that it will increase but just not quite as much as it usually does," Yosemite spokeswoman Kari Cobb told AFP.
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.
On 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.