Hundreds of people have queued for "on the door" tickets to a new Banksy show in Weston-super-Mare.
Thousands struggled to get online tickets to Dismaland, a dark theme park, which is open for five weeks at the seaside resort.
A "locals only" free ticket day was held on Friday, but the ticket website crashed when it received more than six million hits.
General tickets are due to go on sale online again on Tuesday.
Doors opened just after 11:00 BST on Saturday. Many queued overnight in order to guarantee entry into the show.
A message on the Dismaland website said "due to unprecedented demand" it was unable to process online ticket sales, and Saturday and Sunday tickets, costing £3, would only be available on the door.
The site has capacity for 2,000 people, and after that is reached, it will be one in, one out, organisers said.
BBC News correspondent Andrew Plant, who is at Dismaland, said the queue was taking about 4 hours.
Fans have been pondering whether their frustration in failing to buy tickets is in fact part of the "Dismaland experience".
The UKBusinessInsider has questioned the functionality of the Dismaland website, which also shows an upside down supermarket trolley.
At Dismaland: Andrew Plant, BBC correspondent
Queuing is the only way to see Dismaland today. The ticket website is offline until Tuesday.
So hundreds of people started waiting early this morning to pay their £3 and get inside.
By 10:00 BST, there were 2000 people in the line, which snakes round temporary metal fences and looks like the queues for X-factor auditions.
They're called in in groups of ten every few minutes, and then disappear into the double-doors that mark the start of the Dismaland experience.
One family I talked to had rung their relative in Grenoble as soon as they heard about the exhibition. That relative took a plane from the Alps to Luton airport, then a train, then a bus overnight, arriving here at 4am.
When I asked them why, they said simply: "It's a once in a lifetime opportunity. There was no question about making the journey."
So far the queue is taking about 4 hours. It's sunny today and people seem happy.
But there's rain forecast for the next few days, and that is a long time to stand and get wet.
North Somerset Council said it was trying to establish if the difficulty in getting tickets online was a real problem or a deliberate ploy by Banksy.
John Brandler, an art dealer who collects and sells work by Banksy, said it was likely to put off visitors from further afield.
"Where we are, I'm from London, it's a minimum of £80 on a train. To turn up and then find you can't get a ticket, is that good for Weston? I don't think so. I think people will really get annoyed," Mr Brandler said.
However Mike Jackson, the leader of North Somerset Council, was confident people would still flock to the show.
"The queue is already building nicely here, we've estimated the economic benefit (for Weston) is at least £6m, there's a real buzz about the town.
"Virtually everyone you've spoken to here in the town is really excited about this," Mr Jackson told Radio Bristol.
Social media platforms have been awash with speculation that the difficult ticketing was part of the show, where the audience is also part of the art.
Michele Marie tweeted: "I firmly believe the whole debacle was part of the show2, while Paul Vassos tweeted: "To all the punters... ever get the feeling you've been had?"
Dismaland features work by more than 50 artists, including Damien Hirst, Jenny Holzer, Jimmy Cauty and Bristol-born Banksy, who says he chose the venue himself after walking past the old lido six months ago, which had been closed since 2000.
Among the exhibits are a distorted mermaid, a dilapidated fairy castle and a boat pond where all the boats are filled with models of migrants, as well as paintings and a beach ball hovering above upturned knives.
Many are twists on traditional fairground rides - such as a coconut shy featuring anvils, instead of coconuts. Banksy described the show as a "family theme park unsuitable for children".