Festival organisers have apologised after young Soundsplash attendees were forced to wait up to seven hours in the hot sun before being let in,
Up to 8000 teenagers were waiting for a handful of shuttle buses to take them to the event.
Festival organiser Brian Ruawai said rigorous checking for harmful substances caused the delays.
"Other summer festivals had significant amounts of the harmful substances that are known to be circulating in the country at the moment," festival organiser Brian Ruawai said.
"That has meant that our entry processing this year took longer."
Parents have complained on social media about the long wait times for buses, calling the logistical mishap a "shambles".
"Pretty irresponsible - heard about some kids that got really fried in the sun waiting to get 'processed' [sic]," one user commented on a post showing the long queues.
While there's an option to drive in, some attendees were dropped off at the Raglan Airfield where they received wristbands and got their bags checked.
Attendees then travelled 4km on a shuttle bus to Wainui Reserve, where the festival is held.
Video of Raglan Airfield shows a long line of young people waiting to enter the festival.
The NZ Herald reported that many underage attendees vomited on the buses after pre-drinking.
Soundsplash festival is popular with underage teens as those under 18 are allowed to attend without parents.
"As festival organisers, we have a responsibility to keep our young people safe," Ruawai said. "Our searching processes are more rigorous this year for this very reason."