A wildfire raging out of control has caused a state of emergency to be declared in the US state of California, officials said.

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 fire, which started a week ago, closed backcountry hiking in the park, but was not threatening the popular Yosemite Valley region.

The fire grew from 255 sq km to more than 430 sq km overnight and was only two percent contained.

US state struggles to end massive wildfire

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.

The fire was threatening about 4,500 residences, according to the US Forest Service. Officials issued voluntary evacuation advisories for two new towns on Friday, spokesman Jerry Snyder said.

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.

Source: AP