Unlike raging wildfires that have burned vast swaths of the drought-stricken US west this summer, the blazes in Sequoia National Park were not explosive.

Flames were 1.5 kilometres from the Giant Forest, a grove of about 2000 massive sequoias on a plateau high in the Sierra Nevada.

"It's been slow growth," fire information officer Katy Hooper said on Friday.

Lower temperatures and a layer of smoke blanketing the area have been suppressing the flames.

Firefighters have placed a fire-resistant aluminium wrapping around the base of the General Sherman Tree, the world's largest by volume at 1487 cubic metres, as well as some other trees and buildings.

A fire in the region last year killed thousands of sequoias, which grow as tall as high-rises at certain elevations on the western slope of the Sierra Nevada.

But a historic drought tied to climate change is making wildfires harder to fight. Lightning ignited two fires in the park on September 9, officials said. The Colony Fire, closest to the Giant Forest, has grown to just under 13 square kilometres, and the Paradise Fire has scorched nearly 34 square kilometres.

To the south, the Windy Fire grew to nearly 28 sq km, including in the Giant Sequoia National Monument, where it has burned into one grove of sequoias and threatens others.

Sequoia National Park is the second natural jewel to be threatened by wildfires in less than a month.

Lake Tahoe, the alpine lake on the California-Nevada line, was threatened by the explosive Caldor Fire. Containment has now reached 71 per cent.

Meanwhile, a big change in weather is taking shape, with forecasters saying a storm will bring rain to the Pacific northwest and parts of northern California through the weekend.

The rain was not expected to come as far south as Sequoia National Park.

Australian Associated Press