Police are disappointed underage teenage girls were able to buy alcohol at two Palmerston North bars during a sting operation.

They are also upset with the level of drunkenness at the premises, with some patrons losing their balance and falling over at closing time.

Two girls, aged 16 and 17, were observed by a plain-clothes police officer as they tried to buy alcohol at 29 premises during a controlled purchase operation.

They were refused at two supermarkets and two bottle stores, but were able to buy alcohol at two of the 25 on-license premises they visited.

At one of the venues, a bouncer allowed the girls to enter after they said they did not have any identification on them.

Police said staff members and duty managers at both premises had been spoken to after the sales, but it was yet to be determined what action would be taken.

The duty managers and licensees could be referred to the Liquor Licensing Authority, while the staff who sold the alcohol could face prosecution.

Palmerston North police alcohol harm reduction officer Sergeant Glenn Ryan said it was disappointing some premises were continuing to breach the most basic of provisions of the liquor laws.

He said bar staff and duty managers should never solely rely on security staff vetting patrons for intoxication and age.

"Whilst they are generally a good gatekeeper, the overall responsibility for ensuring compliance with the Sale of Liquor Act falls squarely on the shoulders of the duty manager."

Mr Ryan said the premises also showed a "severe deficiency" in their ability to monitor the drunkenness of their patrons.

At closing time, many patrons needed help walking, or lost their balance completely and fell over in the streets.

"It was a very disappointing way to end the night."

- APNZ