Police are not investigating an incident where a man brazenly walked out of an Auckland grocery store with a trolley full of goods without paying for them.

But the supermarket is saying it is using its own security measures to detect and prevent shoplifting.

Last Thursday, a man in his 20s strolled out of a Countdown store in Meadowbank with a trolley crammed full of groceries. When he was stopped by staff who asked for payment he brazenly replied that was not going to.

A Countdown spokesperson confirmed police were not called to the incident but said the supermarket chain had a number of security measures to detect and prevent such criminal acts.

"Unfortunately, theft is a reality in retail from time to time and we have a number of security measures in place to detect and prevent shoplifting," said the spokesperson.

"These include CCTV, security tags on certain items, supervisors at check-outs and security guards at a number of our stores."

Retail NZ chief executive Greg Harford said it was general advice that all retailers should report any criminal activity they spotted to police.

"There is a new National Retail Investigation Unit where police officers look at reports of this kind of crime to find a pattern, and make sure repeat offenders are properly prosecuted and caught.

"If police don't know about crime how will they be able to do anything?"

Harford said retail crime was an issue that was being taken very seriously by the sector.

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"People have been stealing from shops for many years but the volume of such incidents in the past few months has increased substantially.

"Not only that but the level of brazenness of offenders has also increased towards theft, and the attitude towards staff is of entitlement and aggression."

A shopper who saw the event unfold described it as shocking.

"I heard one of the staff say to him, 'You have not paid for those' and the response from the thief was, 'I'm not going to.'

"And he boldly walked out. He did not run, he walked. He appeared confident and relaxed. Obviously an experienced supermarket thief," the witness said.

At first, the shopper, who did not want to be identified, said he was stunned that supermarket workers did not do more to stop the man from leaving, but in hindsight understood their reluctance.

"At the time I found the response to this incident from supermarket management frustrating but on reflection, what can they do?

"There is always the huge fear that a person like this could have a weapon and if he had been physically challenged the outcome could have been disastrous."