Black Rock City (United States) (AFP) - Thousands of revelers stuck in the mud for days at the Burning Man festival in the US state of Nevada were told they could finally trek home on Monday after torrential rain had prompted shelter-in-place orders.

With the sun shining on the colorful makeshift community of 70,000 people called Black Rock City, the roads opened Monday afternoon, kicking off the official exit process known as the "Exodus."

"Exodus operations have officially begun in Black Rock City," the festival said in a statement on its website. "The driving ban has been lifted."

Organizers called on the estimated 64,000 remaining visitors to delay departing from the site -- a dried-up lake bed in a remote patch of the Nevada desert -- until Tuesday to avoid massive congestion on the way out. 

As of early Tuesday morning, organizers said the wait time to leave was around eight hours, and reported an accident causing a road closure the previous night. 

"If you can, please get a good night's sleep and leave later," the organizers wrote on social media. 

Festival-goers had been stranded after torrential rains, described as two to three months' worth in the space of hours, came down Friday night and Saturday, turning the venue into a murky quagmire.

So-called "Burners" wearing trademark outlandish outfits trudged through the thick, sticky mud with plastic bags as boots or with their bare feet.

Some left on foot, hiking for hours in the middle of the night to make it to the nearest road and hitch a ride back to civilization. The closest airport is a three-hour drive away in Reno.

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

The main event was postponed until Monday evening, when local media reported it was marked by fireworks and explosions, to the whoops and cheers of a smaller-than-usual crowd. 

'An amazing burn'

For many attendees, the rain and mud were not enough to spoil the party.

David Packard from the city of South Portland in Maine said other campers let him and his friends into their trailers when it started pouring.

"There was a brief double rainbow that provided us with a lot of energy," Packard said. "My feet are dry and I'm warm. So I'm happy."

Packard also said Burning Man gave him precious time with his brother.

"I had an amazing burn. I got to spend an amazing amount of quality time with my brother," he added. "It was nice to be very close and to get closer this week."

Abandoned camps

But David Date, a participant, complained Monday on CNN about people fleeing and leaving gear and trash behind -- breaking the festival's core principle of "no-trace" sustainability.

"They're leaving their entire campsites behind, ditching their cars, their trash, their tents," Date said. "Everyone's got to stick it out."

All events at the annual counterculture gathering were canceled when rain tore down structures for dance parties, art installations and other entertainment.

Dozens of vehicles, mostly recreational motor homes, were stuck in the mud on the roads out, presenting a major logistical challenge.

Mobile cellphone trailers have been deployed and the site's wireless internet was opened for public access, but connections remained patchy.

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

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.

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.