Manukau's liquor licensing agency is drawing up a list of school ball dates, and will send inspectors to follow buses to after-ball parties in a bid to stop alcohol being supplied to minors.

The agency has vowed to block all "after-balls" supplying alcohol to minors following an early-morning bust at the weekend of a van-load of booze meant for party-hopeful teens.

Principals in the area have given the agency and police a list of school ball dates.

"This isn't something we're just going to do as a one-off," said liquor licensing inspector Paul Radich.

"This is an ongoing approach.

"We've allocated some time over the next three months - because that's traditionally ball season - to find out where as many of these things are and obviously we will be asking the police to take action.

"Once we find out when all the balls are, we'll just be following the buses from wherever the ball is to where they're going."

A Herald story on Friday alerted police that Pakuranga College students were selling $55 tickets for an after-ball to be held at a secret location on Saturday night.

Buses took students from the Ellerslie Convention Centre, where the official school ball was held, to the venue about 12 midnight.

Mr Radich said police found out at 11.30pm that the function was being held at an abandoned warehouse in Alfred St, Onehunga.

They met parents and the organisers of the event at the warehouse, before party-goers arrived, and outlined what charges they could face should they supply alcohol.

"It was at that point that they decided the best thing to do was to remove all the alcohol and turn it into a Red Bull and water party."

Mr Radich said police could lay several charges including unauthorised sale and supply which carries a fine of $40,000 or up to three months in prison for sale and supply of liquor to a minor, and providing a place for the consumption of liquor.

"This isn't a public function. The kids were charged $55 to gain admittance to a function in which they would be supplied with all the alcohol they could drink ... that's sale and supply. The minute you start charging people admission to something it is no longer a private function."

The Herald on Sunday said a large white van full of ready-to-drink spirit mixes and beer, driven by an adult who was said to be the parent of a student, left the venue.

After the alcohol was removed, police cars followed the buses to make sure students still went to the alcohol-free event, rather than elsewhere.

An hour after arriving, students were leaving again, saying it was "lame" without alcohol and they were going to town.

The agency received an email yesterday from college principal Michael Williams who said last week his policy was that groups should not be organising functions afterwards, reiterating the school had nothing to do with the after-ball party.

Police on Wednesday sent a letter to about 40 Auckland high schools saying they would not accept excuses for supplying alcohol to under-18s at parties.

The Auckland City Council's chairman of city development, Aaron Bhatnager, said the council was also acting against after-balls.

"If there's an abuse of the law, we intend to step in to uphold the law as is required.

"The rogue operators - and clearly this is an example of a mini-rogue industry - is something that all licensing authorities I imagine across the country are looking at."