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California crews are battling four wildfires amid a triple-digit heatwave in parts of the state.

The worst damage was in Riverside County in southern California, where the Rabbit Fire has razed nearly 8,000 acres.

It left a woman with severe burns and she had to be airlifted to hospital, CalFire told the Los Angeles Times.

The blazes broke out over the weekend, prompting evacuation orders and warnings in some areas.

The Rabbit Fire began on Friday before spreading quickly to threaten more than 150 structures and close a number of roads.

It has razed 7,950 acres and was 35% contained, said CalFire officials on Monday morning.

What sparked the Rabbit Fire and the three others burning in Riverside County was not immediately clear.

The Reche, Highland and Gavilan Fires - which were smaller - started on Friday and Saturday.

The Reche Fire has burned more than 435 acres and was 85% contained. The Gavilan fire burned 338 acres and was 50% contained.

The Highland fire burned 105 acres and is almost fully under control.

The heatwave has made the job for heavily equipped firefighters even more exhausting than usual.

"At no point do you feel any relief," CalFire deputy chief Lucas Spelman told the ����ý. "It's just hot."

To describe what it felt like, Mr Spelman said: "Put on a winter jacket, snow pants, a beanie, winter gloves, and then strap 50-75lb [22-34kg] on to your back and start doing lawn work."

Temperatures in Riverside County reached 39.4C (103F) over the weekend.

Forecasters have said extreme heat and low humidity may hamper firefighting efforts over the coming days.

Inland areas of south-central California are under an excessive heat warning, amid an intense summer heatwave that has placed one-third of Americans under some form of heat advisory.

Nearly 10,500 acres have been scorched by over 3,030 wildfires across California so far this year, says CalFire.

Miles to the north, in Canada, a second firefighter died over the weekend as that country endures its worst wildfire season on record.