Smoke from a wildfire in and around Yosemite National Park is hampering both suppression efforts and the views sought by holiday weekend tourists.

Park spokeswoman Kari Cobb said smoke from the 2-week-old blaze obscured Yosemite Valley for the first time Saturday. The valley is home to the park's most popular landmarks.

And weather forecasts indicate the dense blanket could stick around until Monday.

Meanwhile, U.S. Forest Service spokesman Mark Healey says firefighting aircraft remained grounded Saturday morning because of low visibility caused by the smoke.

Healey says officials are concerned about a 150-acre spot fire that crossed a road and prompted an evacuation order for homes near the west entrance of Yosemite.

As of Saturday, the entire wildfire has burned 343 square miles, up from 333 square miles a day earlier.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

Smoke from a wildfire around Yosemite National Park is causing problems in the San Joaquin Valley, even as firefighters make advances against the massive blaze.

Winds had been blowing dense smoke plumes northeast into the Lake Tahoe area and Nevada but a shift brought them west down to the San Joaquin Valley floor.

Regional air pollution control authorities issued a health caution for San Joaquin, Stanislaus, Merced, Madera, Fresno and Tulare counties. Residents who see or smell smoke were urged to stay inside, especially people with heart of lung problems, older adults and children.

But in signs of progress, By Friday crews had built containment lines around more than a third of the huge forest fire and officials had lifted evacuation advisories in some small communities in the mountainous area,

Also, a few dozen firefighters were released and more could be sent home in coming days, said Daniel Berlant, spokesman for the California Department of Forestry and Fire Protection. More than 4,800 firefighters remained on the scene late Friday.

"We continue to gain the upper hand, but there's still a lot of work to be done," Berlant said.

The 2-week-old blaze burning in the Sierra Nevada northeast of Fresno has scorched 333 square miles of brush, oaks and pine, making it the largest U.S. wildfire to date this year and the fifth-largest wildfire in modern California records. Containment was estimated at 35 percent.

Evacuation advisories were lifted Thursday in Tuolumne City, Soulsbyville and Willow Springs but remained in place for other communities, and evacuations were still mandatory along the fire's southeastern edge.

About 75 square miles of the fire are inside Yosemite but at some distance from the national park's major attractions, including glacially carved Yosemite Valley's granite monoliths and towering waterfalls.

Park officials expect about 3,000 cars a day to pass through gates during the long Labor Day holiday weekend instead of the nearly 5,000 that might typically show. The fire has caused some people to cancel reservations in the park but those vacancies have been quickly filled, officials said.

"Valley campgrounds are still full and skies in Yosemite Valley are crystal clear," said park spokeswoman Kari Cobb.

A 4-mile stretch of State Route 120, one of three western entrances into Yosemite, remained closed, hurting tourism-dependent businesses in communities along the route.

Costs reached $47 million, including firefighters from 41 states and the District of Columbia and significant aviation resources including helicopters, a DC-10 jumbo jet and military aircraft equipped with the Modular Airborne FireFighting System. Aircraft have dropped 1.7 million gallons of retardant and 1.4 million gallons of water.

The fire started Aug. 17 and its cause remains under investigation. It is expected to keep burning long after it is fully contained, and recovery will be extensive. Some 7,000 damaged trees next to power lines will need to be removed by utility crews and 800 guardrail posts will need to be replaced on Route 120, a fire fact sheet said.