The massive Rim Fire, which since Saturday has been quickly burning though eastern central California, reached a remote section of Yosemite National Park Friday, while firefighters battled to save the Sierra Nevada foothill towns of Pine Mountain Lake, Lake Mather and Groveland.

After starting in the Stanislaus National Forest almost a week ago, the blaze has been growing ever since, quickly becoming one of the biggest active fires in the nation, covering an area of more than 150 square miles. It is among 61 wildfires currently burning across the nation.

The fire is less than two percent contained, reportedly doubling in size overnight Thursday.

The Rim Fire crept into Yosemite territory Friday, mostly west of the park around Lake Eleanor, prompting Gov. Jerry Brown to declare a state of emergency in Tuolumne County on Thursday. The declaration will help free up money and resources to fight the blaze.

The blaze grew exponentially throughout the week, rising from sharply from 16,000 acres Wednesday to 54,000 acres Thursday. By Friday morning the blaze stood at 105,620, the San Francisco Chronicle reported.

"The growth of this fire is just something you don't see often," Lynn Tolmachoff, spokeswoman for the California Department of Forestry and Fire Protection, told the San Francisco Chronicle. "If you get one a year, it's unusual. If you get one every 10 years, that may be the norm."

About 4,500 residences are threatened by the blaze, USA today reported, citing California Department of Forestry and Fire Protection spokesman Daniel Berlant.

"Most of the fire activity is pushing to the east right into Yosemite," Berlant said. The Yosemite Valley -- the iconic tourist destination -- is not currently under threat.

Yosemite remains open to visitors for the time being, but the wildfire has caused the closure of a 4-mile stretch of State Route 120, one of three entrances to the park on its west side.

More than 2,000 firefighters and nine helicopters are employed in the battle of the blaze, USA Today reported, citing the US Forest Service. More than 5,000 structures are threatened; four homes have burned.