UPDATED 7.17PM: Police are hunting for information after threats were made to poison baby food and products with the pesticide 1080.

It follows anonymous letters being sent to Federated Farmers and Fonterra in November of last year.

AUDIO: Mike Clement on 1080 investigation

Small packages of milk powder, which later tested positive for a concentrated form of 1080, accompanied the letters.

The letter-writer also said they would go public themselves if their demand wasn't met by the end of March.

Police Deputy Commissioner Mike Clement says while the threat may be a hoax, it must be treated seriously and a priority investigation is underway.

Police National Headquarters said a full investigation began in November, with an Auckland-based team called Operation Concord involving up to 36 police staff.

MPI's  Scott Gallagher & Police Dep' Commissioner fronting media over 1080 poisoning threat pic.twitter.com/gLmTP1gG7K

— Felix Marwick (@felixmarwick) March 10, 2015

Key says the probability of the threat being carried out is very low, but the implications are very serious so it has to be taken seriously.

"It's a form of eco-terrorism without doubt, so the person's motive is to try and bully the government to stop using 1080."

But Clement insists that this threat is "criminal blackmail" but not terrorism.

"We're not treating it as a terrorism offence. We're treating it as an offence of blackmail."

Fonterra CEO Theo Spierings says this is a despicable, criminal act.

He says the dairy industry has thrown its full weight behind the Government and Police response to the threat.

"Although we understand that the threat is very unlikely to be carried out, we have done everything in our power to ensure the security of our already world class supply chains."

The Ministry of Primary Industries deputy director Scott Gallagher says the government's first priority is protecting the health and wellbeing of consumers.

He says as far as he understands, New Zealand infant formula is as safe today as it was before the threats were made in November.

"The combined Ministry of Primary Industry and industry testing programmes confirm there is no 1080 in infant and other formula.

"We have tested just over 40,000 raw milk and product samples and we have had no 1080 detections."

Gallagher says the ability of anyone to contaminate formula during manufacturing is extremely low.

He says since the threats were made, they've strengthened security measures and enhanced product testing.

The NZX has placed Fonterra, Synlait and A2 on a trading halt.

Fonterra's Theo Spierings says it's far too early to say what the financial impact could be from this 1080 infant formula threat #rtpt

— Alex Mason (@AllieMase) March 10, 2015

Infant Formula Exporters Association Chairman Michael Barnett says the blackmailer is threatening not only our billion dollar dairy industry, but the country's reputation.

"Somebody who is theoretically a lover of the environment and animals would threaten human lives to play politics or to try and win an argument, it is absolutely despicable."

Countdown acting manager Steve Donohue knows the threat will be worrying for customers.

He says they've put additional security place from the time the product arrives in its distribution centres to when it is purchased in stores.

Mr Donohue says as a retailer of infant formula, Countdown is doing everything is can to keep it safe in its supermarkets, and as a result it will take a little bit more time for customers to purchase infant formula.

AUDIO: Barry Soper on the 1080 milk powder scare

The Food and Grocery Council calls the baby formula poisoning threat an attack on 'Brand New Zealand'.

It's condemning whoever is responsible for issuing the threats.

The council has absolute confidence in the safety of the New Zealand food supply.

Lock and key

Infant baby formula is under lock and key at a number of supermarkets around the country tonight.

The products have been pulled off the shelves and locked away.

Customers are having to ask at the counter if they're wanting to buy any.

MPI advice 

If you have any information relevant to the criminal investigation, including product you suspect has been tampered with, call police on 0800 72 36 65 or email [email protected].

If you have any questions about what to feed your baby, call Plunketline 0800 93 39 22. If you have general questions, call 0800 00 83 33 or email [email protected].

What is 1080?

Sodium monofluoroacetate, commonly known as 1080, is a fine white powder. It has a slight odour and taste and is said to dissolve easily in water.

While manufactured 1080 is a highly lethal poison to many species, the active ingredient, fluoroacetate, is identical to a substance that occurs naturally in many poisonous plants.

These plants are found in Brazil, Africa, and Australia.

1080 comes in several forms, usually in small dyed green pellets, but also sprayed with carrot baits, pastes and gels.

How long has it been used here?

1080 has been used in New Zealand for pest control since the mid-1950s and is the only poison registered for aerial drops. It is also used in Australia, USA, Mexico and Israel. However, New Zealand uses about 80 per cent of the world's production of manufactured 1080.

How does it work?

Whether laid on the ground, or dropped from the sky in large remote areas, the 1080 is eaten by the animal.

If enough is ingested, the poison disrupts the process of breaking down food to provide energy for cells to function. Once the animal has run out of energy, it dies from heart or respiratory failure.

Herbivores like possums become lethargic and usually die within 6-18 hours from cardiac failure. Carnivores experience problems with their central nervous systems and may suffer convulsions before dying.

What are the risks?

1080 is extremely toxic to many animals, and dogs are particularly sensitive to it.
In 2007, West Coast man Ryan Fitzmaurice lost his pet Labrador, Tigger, which died after eating a possum that had 1080 in its system.

The possum had been poisoned by a drop near his home.

Mr Fitzmaurice was offered undisclosed compensation by the pest control company. Humans are also at risk if they ingest 1080.

What measures are taken to keep the public and their animals safe?

DoC must meet strict Ministry of Health conditions before getting a permit for a 1080 operation.

DoC must also talk to communities where 1080 operations are planned, let the public know an operation is going ahead and put up signs to show areas where poisoning has taken place.