The heart of Yosemite National Park has been closed as a fierce wildfire burning just to the west jumped fire lines, pouring thick smoke into the valley and forcing visitors to pack up camp and flee.
Heavy black smoke from the Ferguson Fire, which erupted on July 13 in the Sierra Nevada Mountains some 275 km east of San Francisco, prompted park officials to shut down the main visitor hub of Yosemite Valley as well as Wawona and Mariposa Grove.
The smoke reduced visibility and posed health risks to visitors in the popular tourist destination as well as park employees.
The Ferguson, burning in steep, rugged terrain at the western edge of the park that has proven difficult for crews to access, killed firefighter Braden Varney on July 14 when the bulldozer he was using to cut containment lines overturned in a ravine.
Seven other firefighters have been hurt battling the flames, which were 25 per cent contained as of Wednesday. More than 3400 personnel using 16 helicopters and 59 bulldozers were fighting the conflagration.
The blaze is one of some 60 major wildfires burning in the United States this week that have so far scorched an area of about 485,600 hectares. Most are in western states, with blazes also in central Texas and Wisconsin.
As of July 25, wildfires had burned through 1.59 million hectares this year, above the 10-year average for the same calendar period of 1.43 million hectares.
A change in wind direction on Tuesday night drove the flames across southern fire lines, heading toward structures and prompting new evacuation orders in the Lush Meadows area.
High temperatures, fierce winds and arid conditions across the US West on Wednesday at the height of a more than week-long heat wave were expected to increase the danger.
Temperatures above 37 C and winds gusting up to 80km/h are in the forecast for many parts of Oregon, California, Arizona and Nevada into Thursday, the National Weather Service said in a series of advisories.
