A first-hand encounter with synthetic cannabis led Minister of Police Judith Collins to call for a briefing on the substance.

Collins said she came across Kronic while on a foot patrol in central Auckland with Auckland district commander Superintendent George Fraser and area commander Inspector Andy Coster.

"We all smelled what we thought might have been cannabis and tracked it to some young people in Elliott St. They told us it was Kronic, that it was just like cannabis and they got it at a convenience store around the corner."

Collins said they visited the dairy and the wall behind the counter was covered in the fake dope. She said it was the first time she had come across it - "My local dairy to his credit doesn't stock it.

"The shopkeeper told us it was legal and that he was selling quite a bit of it."

A spokesman said the minister was not offered a puff of Kronic and "would not have accepted anyway".

In the briefing, Collins was told Kronic was linked to crime, was difficult to keep from sale and could only be blocked if the Government proved it was dangerous.