The results of the latest controlled purchase operations, conducted by police and the Northland DHB at licensed premises in the Bay of Islands and Whangarei, have dismayed both authorities.
Sixteen and 17-year-old volunteers successfully bought alcohol at four of 11 premises in the Bay of Islands, and four of 23 in Whangarei.
Kerikeri-based alcohol harm reduction officer Senior Constable Graeme Wright described the result as extremely disappointing.
"The four premises involved should have better systems in place regarding not selling alcohol to minors. These sales of alcohol should not be occurring," Mr Wright said.
"All applicants, when they make application for a licence to sell alcohol, state that appropriate systems and procedures are in place to prevent the sale of alcohol to under-age people. Clearly this is not the case for these premises."
Customers who looked under 25 years old and could not produce identification should not be sold alcohol.
"It is important to stress that a full and proper identification check must be carried out, including calculating the [customer's] age," he said.
"This is best practice, and the only sure way to prevent sales to under-age [customers]," Mr Wright said.
"As a community we need to have confidence that licence holders will not sell alcohol to our youth and allow them to drink unsupervised and potentially harmfully."
The consequences of breaching the law were "major", he added, potentially including the suspension of licences to sell alcohol for a number of days.
Sergeant Howard Clement said the results of the operations were poor, given that they had been conducted for more than a decade, alongside education, publicity and enforcement.
"All premises selling or supplying alcohol are aware that we run these types of operations regularly, so should not be surprised that they are being tested," he said.