Police and officials have defended the handling of a threat to poison infant formula, while the results of a tin that may have been tampered are due back within 24 hours.

Photo: RNZ / Kent Atkinson

Police investigating a threat to poison infant formula with 1080 pesticide said yesterday they had received an unspecified number of calls from members of the public who had spotted damage to cans.

Commissioner Mike Bush said one tin was being tested.

"We've had initial analysis and that sample is now winging its way to another location in New Zealand for further analysis," he said.

Mr Bush said at first glance it looked like the damage was caused by a packaging problem in the manufacturing process, but police wanted to make sure it was not related to the threat.

He also defended the investigation after the recent appointment of a new lead investigator, Detective Superintendent Andy Lovelock.

The police had been looking into the threat for the past three months, but Mr Lovelock had only joined the team recently.

Mr Bush said other senior officers had been on the case since the beginning, and it was normal for the team to grow over time.

He said Mr Lovelock was working on other very important matters before being moved.

"No one has asked us to ramp [up] this inquiry. We've had a major focus from the offset and we've put our top investigators on this. We've had absolutely high cover," he said.

"The command of this investigation has been a top priority for us - and for me."

Assistant Commissioner Malcolm Burgess said about 25 officers were on the case in November, compared to about 40 now, which was larger than the average homicide inquiry.

Photo: RNZ / Alexander Robertson

Ministry of Primary Industries (MPI) Deputy Director General Scott Gallacher said the ministry continued to work closely with police.

"They've devoted significant resources to this," he said. "I think that is very clear in terms of the way they have prioritised their staff and resources."

Police Minister Michael Woodhouse was not aware of the recent appointment of Mr Lovelock.

Ongoing vigilance vital - MPI

MPI has urged parents to remain vigilant in looking for infant formula tins that may have been tampered with in the wake of the 1080 poisoning threats.

Ministry officials told MPs today that the number of suspicious tins handed to the police grew by the day.

MPI Director General Martyn Dunne was unable to tell the Primary Production Select Committee exactly how many complaints had been made about infant formula tins people suspected had been tampered with.

"On a daily basis since this became known we've had a number of cans of product that have been handed to the police for them to have a look at it ... I don't know the number ... We're talking small numbers, very small numbers of tins," he told the committee.

All the suspicious tins handed to police so far had been false alarms, he said.

"Most of those have proven to be, in fact at this stage, all of them, so far have tended to be manufacturing line problems, where there have been issues where tins have been damaged.

"There was one case, as I understand it, where the seal at the top had not been fixed and that it is a manufacturing problem."

Photo: SUPPLED

But Labour MP Damien O'Connor told Mr Dunne that MPI's handling of the 1080 poisoning threat made it look like it put trade ahead of food safety.

"But when you delay notifying consumers and therefore giving them the ability to take precautions ... for consideration as you have said - the markets and the New Zealand Dollar. Some people start to think that your considerations as an organisation are first and foremost around trade - not food safety."

Mr Dunne said he disputed that and there had been no delay.

After the select committee, Mr Gallacher urged mums and dads to keep watch for potentially tampering.

"Clearly, police now need the time and energy to now get to the bottom of exactly what has occurred with this very small number of tins which people have fantastically brought to the police's attention."

MPI also informed the select committee that it had sent a team of toxicologists and laboratory technicians to China to help officials there develop their own 1080 tests.