A state of emergency has been declared in California’s Mariposa County after thousands were ordered to evacuate because of a fast-moving wildfire near Yosemite National Park on Saturday.
The Oak Fire exploded into one of the state’s largest wildfires of the year, with officials issuing evacuation orders and shutting off power to more than 2,000 homes and businesses.
The bush fire started on Friday afternoon near the town of Midpines and by Saturday it had grown to nearly 19 square miles (49 square kilometres), according to the California Department of Forestry and Fire Protection.
Evacuation orders are now in place for more than 6,000 people living across a sparsely populated rural area.
“Explosive fire behaviour is challenging firefighters,” said the department, describing the blaze as “extreme with frequent runs, spot fires and group torching”.
The fire had destroyed 10 residential and commercial structures by Saturday morning and was threatening 2,000 others.
It has prompted numerous road closures, including of Highway 140 which is one of the main routes into Yosemite.
More than 400 firefighters are battling the blaze in the Sierra Nevada foothills, armed with water-dropping helicopters and other firefighting aircraft, as well as bulldozers.
The blaze has been fuelled sparked by hot weather, low humidity, and extremely dry vegetation caused by the worst drought in decades, although its initial cause is unknown.
Daniel Patterson, a spokesman for the Sierra National Forest, said that climate change has made the region much warmer and drier over the past 30 years which has led to California experiencing increasingly large and deadly wildfires.
Last year, by August nearly 43,000 Californians were under evacuation orders as a dozen large wildfires raged across the state.
“The fire is moving quickly. This fire was throwing embers out in front of itself for up to two miles yesterday. These are exceptional fire conditions,” warned Mr Patterson.
Residents have been sharing pictures on social media of an enormous pyrocumulus cloud stretching up into the atmosphere.
Andy Bollenbacher, a meteorologist with the US National Weather Service, said that the cloud top has stretched up to 30,000 feet into the sky on Friday night.
The risk is that in extreme conditions wildfires can begin creating their own weather system when the smoke forms a pyrocumulonimbus cloud, similar to to normal cumulonimbus or thunder clouds which produce hail, thunder and lightning.
In the current condition such weather – and the attendant lightning strikes and stronger winds – could cause even more fires in a chain reaction of destruction.