Friends Chloe Murray-Lovell and Bailey Bevey, both 18, turned up about 8.30am.
The pair had travelled to North Shore after Ms Murray-Lovell received two three-slide passes, each $25, for her 18th birthday.
When the gates were due to open at 9, those waiting were told there would be a 30-minute delay, she said.
As more people poured into the carpark area, the gates remained closed.
About 10am, a crew member informed people there was a hole in one of the landing pools and staff were trying to fix it, she said.
The next few hours were just a mess as hundreds of people were herded between being let inside the event area and being shut outside the gates. She estimated up to 1000 people were waiting around at one stage.
"We literally sat outside the gates more than we were inside the gates."
The two students then ran out of time to go on the slide as they had to leave Whitford before midday for the Breakers v Cairns Taipans basketball match at Vector Arena.
"We went early because we knew we had to leave," Ms Murray-Lovell.
"We weren't going to queue for another two hours after they opened the slide [about 11am]."
Torbay father Floyd Webster, who took his two children, aged 11 and 13, and one of their friends, said he would be applying for a refund.
"We queued for two hours and 45 minutes for one slide. It was a total shambles."
His son also became stuck while sliding down and was pushed so hard by one of the staff that he came off his boogie board, then hit another person on the slide, Mr Webster said.
Monster Slide organiser Jamie Templeton said staff worked through the night to try to fix the pool puncture.
"We made a post through Facebook once we realised we would not get it open in time."
Those who attended could apply for refunds through the organisation's website or via email, Mr Templeton said.
While the event had faced other problems in previous venues in New Zealand, including reports of injuries, Mr Templeton was adamant its summer tour would continue.
Meanwhile, six children were hurt on Saturday after an 8m tall inflatable slide tipped at the Masterton A&P show. The youngsters were taken to Wairarapa Hospital and checked over.