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.
The blaze spread into Yosemite National Park on Friday as authorities urged more evacuations in nearby communities where thousands fled during the week as flames engulfed the slopes of the western Sierra Nevada.
The week-old Rim Fire grew to 164 sq miles (424 sq km) by Friday morning, and had burned 17 sq miles at the edge of the park by the afternoon.
The blaze has forced scores of tourists to flee during peak season and is threatening thousands of homes.
More than 2,000 firefighters have been tackling the flames in difficult terrain. It is just 2% contained.
California Governor Jerry Brown has declared a state of emergency.
The fire, which started a week ago, closed backcountry hiking in the park, but was not threatening the popular Yosemite Valley region.
Smoke blowing across the Sierra into Nevada forced officials in several counties to cancel outdoor school activities and issue health advisories, especially for people with respiratory problems.
"Most of the fire activity is pushing to the east right into Yosemite," said Daniel Berlant, spokesman for the California Department of Forestry and Fire Protection.
A spokeswoman for the US Forest Service said 4,500 homes, hotels, businesses and several campsites are under threat as of Friday, up from 2,500 the day before.
Officials have gone door to door in the summer community of Pine Mountain Lake urging people to leave.
A mandatory evacuation order remained in effect for part of Pine Mountain Lake, a summer gated community that is a few miles from the fire line.
The blaze has already destroyed four homes and 12 outbuildings in several different areas, Snyder said.
One firefighter also sustained a heat-related injury.
The Rim Fire is one of 50 major wildfires burning in the western US.