San Francisco - A wildfire threatening northern California's Yosemite National Park was endangering San Francisco's power supply on Saturday as more than 2 600 firefighters struggled in rough terrain to tame the massive blaze.
Only 5% of the so-called Rim Fire is contained, with the Forest Service labelling the potential for further growth as "extreme" given the dry conditions and location in steep canyon areas.
The 518km² fire is scorching the remote north-western edge of Yosemite. The park popular with tourists as a hiking and climbing destination remains open, however.
The Forest Service says 4 500 structures are in danger and evacuations for several nearby communities have been ordered. There have been no reported fatalities.
The out-of-control inferno is also threatening the power grid of San Francisco, some 300km to the west.
California Governor Jerry Brown declared a state of emergency for San Francisco late on Friday, saying transmission lines and other electricity infrastructure serving the city were vulnerable.
The cause of the fire, which began last week, remains unknown.
