Organisers made it clear the event was alcohol-free, the pupil said, but many revellers chose to sneak it in.
The comments came after the school's principal hit out at parents for allowing their children to go to the unofficial ball, which was not sanctioned by the college.
The event - which attracted around 800 people - was held at council-owned Shed 6 on the Wellington waterfront on Saturday night.
Another Wellington College student, who did not want to be named, said it was obvious there were "heaps of people drinking".
"When I rocked up there were some people passed out. I was out to it."
He also said "hundreds were really drunk".
He believed some students snuck in alcohol in their pants.
Earlier today, headmaster Roger Moses said the event was a private function and was a matter for the parents and police, not the school.
"This function had no school input. We did not advertise it. We didn't even know it was on."
He did not have control over what students did outside of school, he said.
"What people don't understand is that school does not have control over students outside of school hours. It's a parent issue, not the school's."
The matter was being dealt with by police, he said, and he would not be speaking to students until police had completed their investigation.
Wellington City Council spokesman Richard MacLean said the venue was hired without a liquor licence.
"There was never any intent liquor would be served or drunk," he said.
About 18 security guards were monitoring the event.
Mr MacLean said he was aware a few students were "passed out" and an ambulance was there to treat and take them to hospital if necessary.
Wellington College has not held an official ball for 20 years due to problems with intoxicated students and Mr Moses said the school would not be changing its stance against balls any time soon.
"I will absolutely not change my mind. Functions like this can turn to custard."
A Wellington police spokeswoman said officers were called to an event at Shed 6 on Queens Wharf.
"Forty-eight young people attending the event required medical treatment for alcohol-related illness or injuries," she said.
Of those 48 students, 37 were understood to be intoxicated and a further 11 needed attention for injuries.
The police spokeswoman said officers continued to monitor the event throughout the night.
Police were still "gathering information" about the event and would "decide on an appropriate course of action once all the facts were known", she said.
Shed 6's management will be reviewing its practices to see how the risk of a repeat incident can be minimised.
Glenys Coughlan - chief executive at Positively Wellington Venues, which is responsible for Shed 6 - said the numbers of those intoxicated and needing medical attention were higher than usual.
Following a recent risk assessment, the company has been looking at a number of improvements, including bringing in breathalysers and ensuring police were kept in the loop around such events.
"We had several meetings with the organisers and the parents where the Health and Safety was outlined very clearly."
As a result of this extra security was on hand, there was a minimum food spend required and Wellington Free Ambulance were on site, she said.
However, despite the higher levels of security a number of students were still able to sneak alcohol in through small Ribena drink packets that are soft and difficult to detect when hidden well, she said.
The company would be meeting with parents and police shortly to "debrief", she said.
-- additional reporting: The New Zealand Herald
NZME sk pd
