Burning Man festival-goers have been told to conserve their food and water after heavy rain turned the campsite into a mud bath.
The weather has been so bad that access in and out of the event in the US state of Nevada has been "halted", organisers said in a statement.
US media reported that more than 70,000 people were stuck there on Saturday.
Held in Black Rock Desert, the annual festival is one of America's most well-known cultural events.
Footage on social media shows attendees struggling to walk on muddy paths.
Organisers have said "no driving is permitted until the playa surface dries up, with the exception of emergency services".
"Participants are encouraged to conserve food, water, and fuel, and shelter in a warm, safe space," they added in a statement.
Before the festival officially started on 27 August it was hit by the remnants of Hurricane Hilary, prompting organisers to close the gates to early arrivals.
Now, after a night of continuous rain, this massive festival is mired in mud - the day before people were due to start heading home.
Given the possibility of more rain tonight, it could be several days before the ground becomes dry enough for vehicles here to leave.
The event usually features giant interactive art installations and a huge wooden man that is burnt at the end of the event.
But one man at the festival told the BBC most events have been called off as they largely take place in the playa - where there is currently no way to get in and out.
Another festival-goer told the BBC that the usual groups of "weekend warriors" - people who only plan to attend at weekends - were not there this year.
Anatoly - who did not want to give his surname - is at the festival with his daughter for the second year in a row.
He said that they had come prepared for dust storms in the usually hot and dusty desert, but had instead been greeted with heavy rain.
"Everyone is fine, but there is an aspect of uncertainty," Anatoly said, as "some people's tents got flooded" and "signal [across the camp] is the problem, we can't really communicate with anyone".
The pair said portable toilets were out of use, as they cannot be emptied due to weather conditions.
They said they were letting tent owners use the family's campervan toilets.
Nonetheless, many here are trying to make the best of it, dancing in the mud to techno music.
One festival-goer who spoke to the BBC, Shervin Natan, said that despite the muddy conditions, "the party's still going, it's business as usual."
"There are worse conditions than this, everyone is helping each other out, that's what Burning Man is all about," he added.
They are used to dust storms here - the motto of Burning Man is "radical self reliance" - but that motto is being put to the test in a way that few of the regular attendees at this event can remember.
Burning Man was founded in June 1986 when Larry Harvey and his friend Jerry Goodell burned a wooden man on Baker Beach in San Francisco to mark the summer solstice.
It was first held in Nevada's Black Rock Desert in 1990.
Festival-goers sometimes interview to get into popular camps and have to prove their commitment to its ideals.
Some groups spend the entire year planning their camp, artwork and theme. But this year there had been worries about the weather and tickets were changing hands on the secondary market at below market rate.
Additional reporting by James Clayton in San Francisco and Azadeh Moshiri.
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