A mass exodus of some 72,000 people stuck for three days at a music festival in the Nevada desert is expected to begin, say authorities.

Thousands of revellers have been trapped at the Burning Man festival since a late-season storm dumped more than 150 millimetres of rain and turned the site into a boggy mess.

Foot-deep mud forced attendees to shelter in place and conserve food, water and other supplies. No working toilets exacerbated the uncomfortable conditions.

The annual gathering at Black Rock City, north of Reno, attracts nearly 80,000 artists, musicians and activists for a mix of wilderness camping and avant-garde performances.

The makeshift city pops up in the desert for the event each year, but roads were closed on Saturday (local time) after an intense burst of rain on Friday.

Authorities said roads could reopen Monday (local time) but the situation was “still difficult”.

“There’s still mud, and there’s still areas that you have to avoid, but slowly but surely we’re working around it,” Black Rock City Superintendent Tony Perez told CNN.

Attendees were trudging through mud, many barefoot or wearing plastic bags on their feet.

US President Joe Biden said in Delaware he was aware of the situation, including one death.

Investigators said the death was unrelated to the muddy conditions.

Australian singer Casey Donovan wrote in an Instagram post on Sunday that she was among the thousands stuck in the muddy tent city.

“We are safe, we have food and ‘dryish’ shelter. It is very moist here and forecast is for more rain over the next few days,” she posted.

“Fingers and toes crossed for some sunshine to clear things up.”

Earlier, DJ Diplo posted a video to Instagram showing him and comedian Chris Rock riding in the back of a fan’s ute. He said they had walked nearly 10 kilometres through the mud before hitching a ride.

“I legit walked the side of the road for hours with my thumb out,” wrote Diplo, whose real name is Thomas Wesley Pentz.

The event began on August 27 and was scheduled to end Monday.

The Reno Gazette Journal reported organisers started rationing ice sales and that all vehicle traffic at the sprawling festival grounds had been stopped, leaving portable toilets unable to be serviced.