The largest grove of giant sequoias in Yosemite National Park has been closed and hundreds of people were ordered to evacuate nearby as a wildfire burning through dense forest became the latest in recent years to threaten the world’s largest trees.

A team is being sent to Mariposa Grove to wrap some of the massive trunks in fire-resistant foil to protect them as the blaze burns out of control.

More than 500 mature sequoias are threatened but there are no reports yet of severe damage to any named trees, such as the 3,000-year-old Grizzly Giant.

The cause of the fire is under investigation and the rest of the park remains open as nearly 300 firefighters try to control the flames, with the help of two water-dropping helicopters and an air tanker dumping flame retardant.

The giant sequoias, native in only about 70 groves spread along the western slope of California’s Sierra Nevada range, were once considered impervious to flames but have become increasingly vulnerable as wildfires fuelled by a build-up of undergrowth from a century of fire suppression and drought exacerbated by climate change have become more intense and destructive.

Lightning-sparked wildfires over the past two years have killed up to a fifth of the estimated 75,000 large sequoias, which are the biggest trees by volume.

Nancy Phillipe, a Yosemite fire information spokeswoman, said there was no obvious natural spark for the fire that broke out on Thursday next to the park’s Washburn Trail.

Smoke was reported by visitors walking in the grove, which reopened in 2018 after a 40 million US dollars renovation that took three years.

The grove, which is inside the park’s southern entrance, was evacuated and no-one was injured.

The fire had grown to 466 acres by Friday evening, authorities said.

Evacuation orders were issued for the grove along with the nearby community of Wawona – which is surrounded by the park – and the Wawona Campground, where about 600 to 700 people were staying in tents, cabins and an historic hotel.

A fierce windstorm ripped through the grove less than two years ago and toppled 15 giant sequoias, along with countless other trees.

The downed trees, along with massive numbers of pines killed by bark beetles, provided ample fuel for the flames, but winds on Friday were calm and the fire was not spreading rapidly.

The park has used prescribed burns to clear brush around the sequoias, which helps protect them if flames spread into the grove.