The Caldore Fire, now one of the largest wildfires in California's history, is inching its way into the outskirts of the Lake Tahoe basin. The California Department of Forestry and Fire Protection said the fire is now the nation's No. 1 priority to put out.

The 10-day-old wildfire has already destroyed nearly 123,000 acres of land since it ignited. Authorities said it has also burned down 632 structures and more than 450 homes. The rapidly spreading wildfire has forced local officials to order an immediate evacuation and the closure of nine national forests.

CAL FIRE said about 18,000 more homes are in danger of being destroyed if the wildfire is not placed under the control. The agency said the fire is still about 11% contained as of Wednesday.

The agency's chief, Thom Porter, said the fire is now "knocking on the door" of the Lake Tahoe basin. He said all of their firefighting resources are now being used to help efforts to put out the fire and keep it out of the basin.

The agency has also committed 2,100 rescue workers, 50 fire crews, 22 helicopters, and 200 fire engines to the effort.  

Porter said the fire is now "the No.1 priority in the nation" due to its proximity to residential areas and public infrastructures. He said it is possible that the fire could spread to the South Lake Tahoe area, which is a popular vacation stop near the California-Nevada border.

On Wednesday, thick yellow smoke spread throughout Lake Tahoe, which had also been blanketed by ash. Tourists and residents in the area have been warned of hazardous air and advised to remain indoors if possible. Tourists attractions, including the gondolas that ferry passengers to the summit of Heavenly Mountain, have been closed.

Roads leading to Lake Tahoe, including Highway 50, have temporarily been closed. Firefighters have been working to keep the blaze from crossing the highway.

"We are working 24 hours a day with adequate personnel to make sure that people are safe. There is plenty of planning. We are going to keep the community safe. That's our job," El Dorado County Sheriff's Office Spokesman Sgt. Eric Palmberg said.