LOS ANGELES (AFP) - More than 2,000 firefighters battled a massive wildfire in California on Tuesday (July 3) as authorities warned that record-breaking heat expected by the weekend could spark more blazes.
The so-called County Fire in the northern part of the state had scorched 70,000 acres (28,327 hectares) in Napa and Yolo Counties by Tuesday and was just five per cent contained, fire officials said.
Authorities late Monday had warned residents in several counties to be ready to flee if fire conditions worsen.
The fast-moving blaze, which has not caused deaths or injuries, erupted last Saturday west of the capital, Sacramento, and quickly spread southward.
The smoke and ash from the flames turned the skies orange and prompted the San Francisco Department of Emergency Management to issue an air quality alert on Sunday, urging the elderly, children and people with heart conditions to avoid physical activity.
Fire crews in the state are also battling another blaze, dubbed the Pawnee Fire, which by Tuesday morning was 80 per cent contained.
Cal Fire spokeswoman Tricia Austin told AFP that 14,900 acres (6,030 hectares) in Lake County, north of San Francisco, had been eaten up by the fire which also destroyed 22 structures.
Austin said fire crews hope to extinguish the blaze by the weekend.
She said the wildfire season had begun earlier than usual this year, forcing crews to be on the alert all the time.
"We're becoming, where it's not just fire season (typically in September and October), we're always having to be prepared," she said.
Officials are bracing for more wildfires heading into the July 4 Independence Day holiday during which many people set off illegal fireworks and have campfires.
The National Weather Service has also warned that triple digit (Fahrenheit) temperatures expected in the southern part of the state starting Friday could result in "critical fire weather conditions."
California Governor Jerry Brown said in a statement on Monday that more land had burned in California in the first six months of this year than during the same period last year.
"Cal Fire has already fought more than 53,000 acres of wildfire this year compared to an average of 23,000 acres over the same time in previous years," he said.
Experts say that the wildfires are being driven by heat, dry conditions and some 129 million trees that have died in recent years because of drought and insect attacks.
Elsewhere across the western part of the United States fire crews this week were also battling several wildfires in Colorado, Utah, Washington and Oregon.