The Rim Fire on Saturday grew to nearly 200 square miles, which is about 128,000 acres. Containment is at 5 percent.
The fire is burning toward the Hetch Hetchy reservoir, where San Francisco gets 85 percent of its water and power for many of its buildings. Gov. Jerry Brown on Friday declared a state of emergency because of the threats.
The blaze started in a remote canyon of the Stanislaus National Forest last Saturday. More than 4,500 homes are threatened and four have been destroyed. Thousands of people in communities near the park have been evacuated.
The fire has grown so large and is burning dry timber and brush with such ferocity that it has created its own weather pattern, making it difficult to predict in which direction it will move.
"As the smoke column builds up it breaks down and collapses inside of itself, sending downdrafts and gusts that can go in any direction," said Cal Fire spokesman Daniel Berlant. "There's a lot of potential for this one to continue to grow."
After burning for nearly a week on the edges of Yosemite, the fire moved into the northwest boundary of the park on Friday. Yosemite Valley, the part of the park known for such sights as the Half Dome and El Capitan rock formations and waterfalls, remained open.
More than 2,600 firefighters and a half dozen aircraft are battling the blaze.
Several outdoor events, including the Strawberry Music Festival, have been canceled due to the fire.
A four-mile stretch of State Route 120, one of three entrances into Yosemite on the west side, remains closed because fire has burned on both sides. Two other western routes and an eastern route were open.
The Associated Press contributed to this report.