US rally driver and YouTube star Ken Block was killed when the snowmobile he was riding overturned on a steep slope in Utah, his racing team and US media reported Monday.

"It's with our deepest regrets that we can confirm that Ken Block passed away in a snowmobile accident today," Hoonigan Racing Division said on its web page.

"He will be incredibly missed."

TMZ Sports reported that Block, 55, was riding a snowmobile on Monday afternoon when it "suddenly upended" and landed on top of him.

He was pronounced dead at the scene, it quoted the Wasatch County Sheriff's Office as saying.

The sheriff's office said Block was alone when the accident occurred. He had posted pictures on his Instagram page earlier on Monday.

Block was an action sports star who co-founded the skateboard brand DC Shoes in 1994 and began his rally-driving career when the company was sold 10 years later.

He became more widely known after posting his 10-part Gymkhana video series on YouTube, which featured him stunt driving on dangerous tracks and obstacle courses.

According to ESPN, his videos were viewed more than a billion times and his Hoonigan YouTube channel became the most popular in motorsports history.

Block also competed in snowboarding and motocross.