SACRAMENTO/LOS ANGELES (REUTERS, AFP) - California Governor Gavin Newsom declared a state of emergency in five counties on Sunday (Sept 6) due to wildfires.

The counties included Fresno, Madera, Mariposa, San Bernardino and San Diego, the governor's office said in a statement on Sunday.

The declaration was prompted by the Creek Fire that started last Friday night and rapidly grew to burn some 18,210ha, forcing evacuations and road closures in the Fresno area in central California.

Eight people have been killed and some 3,300 structures have been destroyed over the past three weeks in wildfires across the state.

Over 200 people were airlifted to safety overnight after a fast-moving wildfire cut off the only road out of the Mammoth Pool Reservoir, a popular recreational site in California's Sierra National Forest.

Meanwhile, the fire in San Bernardino was triggered by a firework at a gender reveal party.

More than 500 firefighters and four helicopters were battling the El Dorado blaze east of San Bernardino, which started last Saturday morning, California Department of Forestry and Fire Protection (Cal Fire) said.

Residents of several communities in the area have been ordered to evacuate.

"Cal Fire Law Enforcement has determined the El Dorado Fire, burning near Oak Glen in San Bernardino County, was caused by a smoke generating pyrotechnic device, used during a gender reveal party," Cal Fire said on Twitter.

"Those responsible for starting fires due to negligence or illegal activity can be held financially and criminally responsible," it warned.

Gender reveal parties are held during pregnancy to unveil the sex of the expected child, sometimes announced by pink or blue smoke fireworks.

Record temperatures over the three-day Labour Day weekend have aggravated already dangerous fire conditions and further stressed exhausted California firefighters.

Temperatures reaching more than 43 deg C were forecast for the Los Angeles area on Monday.