Alton Towers has closed after its water supply was disrupted by an electrical storm.
The Staffordshire theme park said it was "closing gradually", following the storm in the early hours, and asking people to leave "at their leisure".
Dozens of people reacted on Twitter criticising the park for not issuing the announcement sooner.
A spokesperson said it was working to fix the problem. The theme park is due to re-open as normal on Thursday.
The resort's hotels and waterpark were unaffected by supply issues and it was revalidating tickets for visitors whose experience had been disrupted, the spokeperson added.
The announcement advising people not to visit the park was posted on Twitter shortly after 12:00 BST, sparking a furious response from some visitors, including one who said she had travelled for over three hours to get there.
Maxine Woodward arrived on Tuesday and said there was "chaos" on Wednesday morning.
She and her family left "having missed out on many of the rides".
"Overall, we wasted a journey and holiday days from work," she said.
"It just felt like they hoped they could fix it and were willing to let thousands of people in, taking ticket money."
A member of staff, who wished to remain anonymous, said park staff were only made aware of the scale of the problem by 11:00 and were told to close the rides about an hour later.
She told the BBC workers had to hand out bottled water to visitors and mobile toilets were made available, but communications across the park led to a sense of confusion.
The resort apologised for any inconvenience and said it hoped to "reopen shortly once the water supply has been restored".