For the first time since the blaze broke out in a neighboring forest two weeks ago, smoke obscured Yosemite Valley, home to the park’s most popular landmarks, spokeswoman Kari Cobb said.

“I’m in Yosemite Valley right now, and I cannot see the cliffs around me,” Cobb said. “The wind has shifted and smoke is impacting the entire park. We have been lucky until now.”

All the campgrounds in the Valley still were full as of Saturday morning, despite the thick blanket and burning smell that permeated the area and was expected to linger until at least Monday, she said.

As a health precaution, visitors were being asked to scale back their outdoor recreation plans and avoid strenuous activities or even stay indoors.

Meanwhile, firefighting aircraft were grounded most of the morning because of low visibility caused by the smoke, U.S. Forest Service spokesman Mark Healey said. The blaze had scorched 343 square miles of brush, oaks and pines and 11 homes, as of Saturday, an area larger than the cities of San Francisco, Oakland and San Jose combined.

Of that total, 94 square miles of wilderness have burned in the northern section of Yosemite, up from 75 square miles a day earlier.

Although containment efforts proceeded on a positive note overnight, officials were concerned Saturday about a 150-acre spot fire that crossed a road and prompted an evacuation order for homes near the west entrance of Yosemite, Healey said.

Once planes and water-dropping helicopters were cleared to take off again, the worry lifted some along with the evacuation order.

“Air operations are going full-blast to bring this fire under control,” Healey said late Saturday afternoon.

The cause of the fire, which started and has claimed the most acreage in the Stanislaus National Forest, is under investigation.

Healey said fresh firefighters were being brought in to replace tired crews, but that officials did not plan to reduce the nearly 5,000 people assigned to the blaze.

The wildfire is the largest now burning in the United States and is the fifth-largest in California history.