San Francisco, Aug 17 (IANS): The US National Weather Service (NWS) has issued a rare fire tornado warning for the state of California after a pyrocumulonimbus cloud formed out of huge raging wildfire.

Intense wildfires can sometimes create their own weather, resulting in the formation of a pyrocumulonimbus cloud due to the intense heating of the air which cools and condenses as it ascends, reports Xinhua news agency.

On rare occasions, this situation can lead to the formation of a fire tornado.

"Tornado warning issued on the #LoyaltonFire near Roberts Canyon. Heed all orders by emergency managers and responding personnel. Stay away from the fire area," the NWS tweeted on Sunday.

The warning indicated that the area of the possible fire tornado had zero population, but it was an extremely dangerous situation for firefighters.

As of Sunday, the Loyalton Fire, which was first reported on Friday afternoon near the border line between the states of California and Nevada, has already burnt 20,000 acres and is only 5 per cent contained, according to InciWeb, an interstate incident information system.

More than 400 firefighters are fighting the blaze.

Fueled by record heat waves, wildfires raging in California, Oregon and Colorado have scorched 100,000 acres this weekend.

A 2018 fire tornado that formed out of the Carr Fire in Northern California killed a firefighter and a heavy equipment operator.

A team of meteorologists from NWS launched investigation to the incident and found it had winds up to 230 kph.

Scientists use the Enhanced Fujita scale to rank the strength - wind speed and destructive force - of tornadoes on a 0 to 5 scale. Fewer than six in every 100 reach an EF-3 or higher in the US.

The 2018 fire tornado was identified as a powerful EF-3.