A controlled burn ignites pine trees on the "Rough Fire" —
A controlled burn ignites pine trees on the "Rough Fire" —

A wildfire raging in California's Kings Canyon National Park forced the evacuation of about 20 homes and a heat wave prompted concern that the blaze will continue to spread, authorities said on Tuesday.

At 98,000 acres (40,000 hectares), the so-called Rough Fire is the largest wildfire currently burning in California, the U.S. Forest Service said, as the state wilts under a heat wave expected to bring temperatures over 100 degrees Fahrenheit (37 Celsius).

The Rough Fire cast smoke over numerous popular hiking and camping area in the southern part of the Sierra Nevada mountains near Fresno, prompting cancellation of tours and other activities. All campgrounds in Kings Canyon National Park were closed for the Labor Day weekend and remained closed on Tuesday.

The park and adjacent national forest land are home to some of California's most famous giant Sequoia trees. Grant Grove, where the giant General Grant tree is located, was open on limited basis on Tuesday, but the area was likely to be smoky, said Jim Schwarber, a spokesman for the U.S. Forest Service.

The fire also is affecting Sierra National Forest and Sequoia National Forest, which has the largest concentration of giant Sequoia trees in the world, according to the U.S. Park Service.

The heat predicted for much of the state this week could exacerbate fire conditions, particularly if the winds pick up, Schwarber said.

"The weather conditions are going to continue to support active fire behavior and there is the potential to have extreme fire behavior if higher winds develop," Schwarber said.

Officials issued extreme heat advisories in part of California as temperatures climbed into the high 90s, with relatively high humidity for the region, and expected to climb as the week wears on.

As of Tuesday morning, winds were relatively light at 5 to 10 miles per hour (8-16 kph), and were not immediately expected to pick up this week, the National Weather Service said.

Tony Botti, a spokesman for the Fresno County Sheriff's Deparment, said about 20 homes have been evacuated. The homes are located in a sparsely populated area in the forest, according to Schwarber.