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As wildfires rage across California, all national forests in the state will be closed to visitors starting Tuesday, according to an internal memo from the U.S. Forest Service obtained by The Sacramento Bee.

The closures will begin at noon Tuesday and will extend through at least Sept. 17 — including for the upcoming Labor Day holiday, according to the Monday announcement.

“I have made the difficult decision to temporarily close all (California) National Forests in order to better provide public and firefighter safety due to extreme fire conditions throughout the state, and strained firefighting resources throughout the country,” California’s regional forester, Jennifer M. Eberlien, said in the notice to employees, according to the Bee.

All 20 million acres encompassing the state’s national forests will be closed to camping, hiking and all other activities. In Southern California, that includes the Angeles, San Bernardino, Los Padres and Cleveland national forests.

“I do not take this decision lightly but this is the best choice for public safety,” Eberlien said in the memo. “It is especially hard with the approaching Labor Day weekend, when so many people enjoy our national forests.”

The Forest Service hadn’t made any public announcement about the closures by late afternoon Monday, but news was getting out on social media. Some people were reporting getting notices that their wilderness reservations were canceled. Mammoth Mountain, which is on Inyo National Forest land, said its facilities would be shutting down due to the closures.

A closure was already in effect for nine national forests in Northern California as more than a dozen large fires blaze across the state.

On Monday, thousands of people were being forced to evacuate from South Lake Tahoe as the Caldor Fire raced toward the resort city between California and Nevada. The blaze had scorched at least 277 square miles since breaking out on Aug. 14.

In the Cajon Pass area, the Railroad Fire closed a section of the 15 Freeway Sunday as winds pushed the blaze across lanes.

Evacuation orders were also in place along the border of San Diego and Riverside counties after a wildfire, dubbed the Chaparral Fire, spread through the Cleveland National Forest on Saturday. It was 13% contained as of Monday.

There are currently more than 15,000 personnel working to put out fire across the state, Cal OES officials said in a press briefing Monday.

Check back for updates to this developing story.