YOSEMITE NATIONAL PARK, Calif. – A wildfire burning for weeks in the backcountry of Yosemite National Park grew unexpectedly, forcing the helicopter evacuation of about 100 park visitors.

Park spokeswoman Kari Cobb said some of the evacuees Sunday included hikers who had climbed the park’s iconic Half Dome peak, rising nearly 5,000 feet above Yosemite Valley. Others had to be airlifted from campgrounds and hiking trails in the area.

Roads into the park remained open, but several trails were closed.

Firefighters had monitored and controlled the lightning-sparked fire that started several weeks ago between Little Yosemite Valley and Half Dome, Cobb said. But the flames were fueled by strong winds and high temperatures Sunday.

“We just got unbelievable crazy winds and unexpected hot conditions,” Tim Ludington, the park’s chief of roads and trails, told the Fresno Bee. “The fire behaviour totally changed.”

The fire burned at least 700 acres, with no containment established. Cobb said firefighters were hampered by the rugged, inaccessible terrain.

About 15 miles southwest of the park, firefighters were slowly gaining the upper hand on a wildfire near the town of Mariposa.

The 300-acre blaze was 70 per cent contained, and an evacuation order already has been lifted for the 300 homes most threatened by the fire, the California Department of Forestry and Fire Protection said. A portion of Highway 49, a main entrance into the park, was briefly closed.

The fire broke out Friday afternoon and threatened a total of 700 homes and five businesses.

Steep terrain in the area and the dry conditions brought on by California’s drought initially hampered firefighters, one of whom received a minor injury Friday, officials said.

Meanwhile, in far Northern California, firefighters increased their control over a blaze that broke out nearly a month ago and despite it growing to 151 square miles. U.S. Forest Service officials said Sunday that no structures have been damaged, and the fire was 30 per cent contained.

The Siskiyou County Sheriff’s Department on Saturday night issued an evacuation advisory for an undetermined number of residents in a neighbourhood newly threatened by the fire. The residents weren’t required to leave but advised to prepare to evacuate.

Forest Service officials estimate that $54.7 million has been spent and nearly 2,700 people used to fight the fire.

100 visitors evacuated by helicopter from Yosemite as wildfires spread