So far this year, more than 150 IDs - driver's licences, passports and 18+ cards - have been seized by door staff after attempts by underage teenagers to get into licensed premises.
"It is certainly more than the previous year," alcohol harm reduction officer Sergeant Ian Paulin said.
The problem of presenting altered IDs or another person's identification was particularly associated with student cities, such as Dunedin and Palmerston North, and was worse around Orientation Week, he said.
In some cases, licences were altered by people scratching the "4" in 1994 to make a "1", while forged licences had been presented in other cases.
"Some are pretty average, like a colour photocopier has been used in the alteration, while some can be very good and have the look and the feel of a licence but without the watermark."
The more "horrendous" fake IDs included generous dollops of white-out pen covering the underage birth date.
He was confident no-one was producing them professionally.
Some teenagers were using older licences, such as a learner's licence, or using a duplicate licence after "losing" their old one, Sgt Paulin said.
"It costs them $35 and they end up with a new licence. They can alter one or if they are over 18 they can give one to a friend or a sibling, so you end up with a lot of licences that have been superceded."
In some cases, the photo looked nothing like the person who presented the licence. The largest cohort of offenders tended to be 17-year-old female tertiary students.
"The ones I have prosecuted so far this year has been the 17-year-olds wanting to go into the bars with their 18-year-old mates, and there was a bit of peer pressure to get in and so they made the decision to alter their licence."
Parents would be well advised to check their teenagers' IDs, in case their sons or daughters were using falsified identification, he said.
Sgt Paulin praised the vigilance of the city's door staff who confiscated any identification that had been falsified or which did not belong to the person.
"Wherever possible, we prosecute. This year we have been arresting people we have caught for altering driver's licences."
