A possible 1080 contamination scare was discovered by supermarket workers in Dunedin last night.
A tin of infant formula with holes in the aluminium seal was found by staff at a Dunedin supermarket about 7pm, police said.
The tin would be seized by Dunedin police and handed on to the team responsible for investigating the threat to contaminate infant formula with the pesticide 1080, Senior Sergeant Jared Kirk said.
Police did not know the level of risk the tin posed and would be ''dealing with it on its merits''.
Authorities are no closer to determining if the threat to poison baby formula with 1080 was a hoax, or who wrote the blackmail threats - despite more than 30 staff working on the investigation.
Police confirmed last night earlier samples of infant formula sent for further analysis tested negative for 1080.
The infant formula in those tins was safe for infants to consume, a police spokesman said.
The test results confirmed the police view that issues highlighted by the public arose from normal manufacturing or handling issues.
However, police urged the public to contact them if they suspected a tin had been tampered with.
''It is good to see the public being vigilant and raising issues of concern,'' the spokesman said.
Phil Rennie, secretary for Primary Industries Minister Nathan Guy, said there had been ''quite a few'' reports of tins potentially tampered with.
''People should go straight to police,'' he said.
He confirmed one of the tins which tested negative for 1080 was found in Christchurch.
A spokeswoman for the Dunedin supermarket where the latest tin was discovered said the supermarket had taken extra steps to increase security around infant formula.
''This includes moving the product to another part of the store ... so it can be monitored either in person or by CCTV,'' she said.
''We have encouraged all customers to speak directly to the police if they suspect a product has been tampered with. We're co-operating with MPI and the police.''
Snr Sgt Kirk said a decision on what testing the tin would undergo would probably be made today.
''It's wait and see what happens,'' he said.
''We need to cross our t's and dot our i's. We don't know - we just don't know.''
Assistant Commissioner Malcolm Burgess said 30 to 40 people were now working on Operation Concord, up from 20 to 25 at the start of the investigation.
''Inquiries by their nature become bigger and you put more people into them,'' Mr Burgess said.
Letters with a lethal dose of 1080 powder were sent to Fonterra and Federated Farmers in November.
The letters contained a threat to contaminate infant and other formula with 1080 if the poison, used to kill invasive pests, was not banned by the end of this month.
