Tens of thousands of festivalgoers were stranded Sunday in deep mud in the Nevada desert after rain turned the annual Burning Man gathering into a quagmire, with police investigating one death.

Video footage showed costume-wearing "burners" struggling across the wet gray-brown site, some using trash bags as makeshift boots, while dozens of vehicles became stuck in the sludge.

Many events at the counterculture festival, which drew some 70,000 people, were canceled when rain tore down structures for dance parties, art installations and other entertainment.

Police said they were probing one death, without giving further details.

Fear set in among some attendees desperate to flee the muddy site.

"I got scared with what happens when so many people run out of toilet paper and water and food, so I felt I had to get out," Pascale Brand, a 40-year-old who arrived from the Netherlands, told AFP.

Brand said she had been "crying a lot," before deciding on Sunday that "I am leaving no matter what."

She got a seat in a neighbor's vehicle and they made it down a muddy road without any problems.

"There were people yelling at you, 'You can't leave... Go back! The gates are closed,'" she said, but the vehicle made it past an unmanned gate, and to a paved road.

"I felt like I was breaking out of something," Brand said.

Others made the strenuous journey on foot.

"It was an incredibly harrowing six-mile (10 kilometer) hike at midnight through heavy and slippery mud, but I got safely out," lawyer Neal Katyal said on social media.

Organizers asked festival crowds to hunker down at the Black Rock City venue after the heavy rains started Friday night. Scattered showers continued throughout the weekend, and it rained for two hours Sunday.

"You can't really walk or drive," a young circus performer named Christine Lee said on TikTok, adding that the mud was five inches deep in some areas.

- 'Water and hope' -

A video posted on social media showed comedian Chris Rock hitching a ride in the back of a pickup truck after managing to leave.

Festival organizers urged so-called "burners" to "conserve food, water and fuel, and shelter in a warm, safe space," saying the "playa" -- the huge open-air esplanade where the event unfolds -- was impassable.

"Look out for your neighbors, introduce yourself," they added.

One attendee, known on the playa only as Dr T, told AFP he is planning to "just go with the flow, meet people and make the best out of this difficult situation."

The California surgeon said he was worried about missing patient appointments Tuesday, but that there was "nothing I can do about it right now."

"We have water, and we have hope and we take people (into) our camp when they need" it, he added.

Organizers insisted early in the day that the event's finale attraction -- the burning of a structure known as "the Man" -- was set to go ahead Sunday night. But the event was later postponed.

"Due to rain & muddy conditions Sunday & an inability to move heavy equipment & fire safety onsite, the Man Burn will not happen tonight," festival account @bmantraffic tweeted.

"It is now scheduled for Monday 9/4, at 9 pm" (0400 GMT Tuesday), it said.

The gathering was originally scheduled to conclude on Monday.

- 'Survival guide' -

Organizers warned that only some four-wheel drive vehicles with all-terrain tires were able to move.

"Anything less than that will get stuck. It will hamper exodus if we have cars stuck on roads," they said on a "2023 Wet Playa Survival Guide" special webpage.

If necessary, they said it would be possible to walk to the nearest road, where buses would be provided to take people to Reno.

Passengers on those buses counted at least 25 vehicles, mostly recreational motor homes, stuck in mud on the roadways out.

Mobile cellphone trailers were being deployed and the site's wireless internet was opened for public access.

According to a White House official, President Joe Biden had been briefed on the situation in the desert.

"Event attendees should listen to state and local officials, and event organizers," the official said.

Last year, the festival contended with an intense heat wave and strong winds.

Launched in 1986 in San Francisco, Burning Man aims to be an undefinable event, somewhere between a celebration of counterculture and a spiritual retreat.

The festival -- for which tickets cost hundreds of dollars -- culminates each year with the ceremonial burning of a 40-foot (12-meter) effigy.

It has been held since the 1990s in the Black Rock Desert, a protected area in northwest Nevada, which the organizers are committed to preserving.