Firefighters are wrapping fire-resistant blankets around ancient trees as blazes tear through California's world-famous Sequoia National Park.
Officials fear the fire could reach the Giant Forest, a grove of some of the world's biggest trees, within hours.
The forest hosts some 2,000 sequoias, including the 275ft (83m) General Sherman, the biggest tree by volume on Earth and about 2,200 years old.
The Colony and Paradise fires have been growing for a week.
More than 350 firefighters, along with helicopters and water-dropping planes, have been mobilised to battle the blazes.
They have wrapped several trees, including the General Sherman, with aluminium foil to protect them.
"It's a very significant area for many, many people, so a lot of special effort is going into protecting this grove," Sequoia and Kings Canyon National Parks spokesperson Rebecca Paterson told the LA Times.
By volume, the General Sherman is the largest known living single-stem tree on Earth and is estimated to be at least 2,200 years old.
Experts say sequoia trees are very fire-resistant and have evolved to survive flames.
Sparked by lightning, the Paradise and Colony fires have been growing across rugged shrubland in the Sierra Nevada.
The fires are the latest in a long summer of blazes in California.
More than 7,400 wildfires have burned in the state this year, scorching more than 2.2 million acres.
They have been driven by higher temperatures and extreme drought conditions. Climate change increases the risk of the hot, dry weather that is likely to fuel wildfires.
The Dixie fire, the second-largest ever recorded in California, has now been largely contained.