California, Nevada worst hit as fires rage through US West

A 25,000-acre wildfire in central California threatened hundreds of homes and businesses today after forcing the evacuation of about 5,000 residents.

It was just one of 46 active large fires spread across 12 states in the American West, with 11 new blazes reported on Tuesday alone, according to National Interagency Fire Center website.

Tall grass from a deluge of winter rains is fuelling wildfires throughout the Western US, damaging more than a dozen homes in Nevada and forcing residents from communities on the outskirts of Yosemite National Park in California, authorities said Tuesday.

Yosemite remains open to visitors, but flames threaten more than 300 homes and buildings in mountain communities southwest of the park, clearing out the small town of Mariposa.

The fire burning since Sunday also puts at risk powerlines providing electricity to the park, and it has closed roads travelled by tourists, officials said.

Around 4.4 million acres have been burnt since the start of 2017, compared to 2.7 million acres in the same period last year, the NIFC said.

Dry and windy conditions have fuelled the wildfire season and thousands of people have been evacuated, including in Oregon and Nevada.

Firefighters managed to contain 5 per cent of California's Detwiler fire, which threatened 1,500 structures in tiny foothill communities in the Sierra Nevada mountains, authorities said. Around 2,000 residents were ordered to flee Mariposa, California on Tuesday.

"Going to bed unsure whether Mariposa, my sweet hometown, will exist when I wake up," resident Jennifer Paquette said on Twitter late on Tuesday.

A total of 5,000 residents were forced to evacuate several small communities southwest of Yosemite National Park since the fire began on Sunday, the California Interagency Incident Management Team said in a tweet.

No injuries were reported as of Tuesday night, according to Cal Fire.

Photographs and videos posted on social media showed empty downtown streets in Mariposa and ash falling from the sky as an orange and pink glow hovered on the horizon during dusk on Tuesday evening.

"It has been terrifying to be honest. I have been crying a lot today," resident Tarah Eastwood told a CBS affiliate on Tuesday.

At least two of the five area Red Cross evacuation centers were at capacity late on Tuesday, according to social media posts.

Governor Jerry Brown declared a state of emergency for Mariposa County on Tuesday as the fire was approaching. The proclamation sends resources to the area.

Record rain and snowfall in the mountains this winter was celebrated for bringing California's five-year drought to a near-end, but it has turned into a challenge for firefighters battling flames feeding on dense vegetation, officials said.

"There's ample fuel and steep terrain," said California Department of Forestry and Fire Protection spokeswoman DeeDee Garcia. "It makes firefighting difficult."

Smoke from the fire in Mariposa County has drifted more than 150 miles away to Reno.

In a remote northeastern corner of Nevada, roughly 14 homes were damaged or destroyed by a wildfire that started Monday. Officials have lifted an evacuation advisory, allowing hundreds of people to return home and assess damage, authorities said.

In Nevada, wind is driving the flames through invasive cheat grass - growing twice the norm, US Bureau of Land Management spokesman Greg Deimel said.

"It is very thick, very dense," he said. "You get the winds and the density of the grass, the fire just goes."

This summer's high temperatures follow a very wet winter that dumped more than 60 feet of snow at ski resorts in the Sierra west of Reno.