'Eco-terrorist' threat to poison New Zealand baby formula

New Zealand has received an "eco-terrorist" threat to poison baby formula, Prime Minister John Key said Tuesday, in a scare that risks further denting the country's "clean, green" reputation.

Police said they were taking the issue seriously after small packages of baby formula containing poison were sent with anonymous letters to the National Farmers Federation and dairy giant Fonterra.

"Whilst there is a possibility that this threat is a hoax, we must treat the threat seriously and a priority investigation is underway," deputy commissioner Mike Clement said.

New Zealand police said small packages of baby formula containing poison had been sent with anonymous letters to the National Farmers Federation and dairy giant Fonterra ©William West (AFP/File)

Authorities warned parents to examine packaging for signs of tampering and supermarkets removed formula cans from shelves to storerooms so shoppers could not access them directly.

Police said the motive behind what they termed a blackmail attempt was the use of a poison called 1080 for pest control, which some critics say kills native wildlife.

Asked how he would characterise the threat, Key replied: "It's a form of eco-terrorism without doubt.

"The person's motive is to try and bully the government into not using 1080 (but) the reality of anyone carrying out this threat are extremely low," he added.

Even if it was a hoax, the scare comes at a sensitive time for New Zealand’s dairy industry, which is recovering from a botulism scare last year involving Fonterra.

It was eventually declared a false alarm but not before potentially toxic formula was yanked off shelves from China to Saudi Arabia.

New Zealand is the world's largest dairy exporter and infant formula is a major component, with annual exports to China alone totalling NZ$3.0 billion (US$2.2 billion).

Infant Formula Exporters Association chairman Michel Barnett said the industry did not need another crisis.

"This could be extremely damaging for New Zealand's exports offshore," he told TVNZ.

"Not just dairy, not just milk formula, our whole reputation as an exporter of food is at risk as a result of this nutter."

The New Zealand Food and Grocery Council said extra testing had been introduced to reassure parents, adding that it had "absolute confidence" that products were safe.

"This is an attack on Brand New Zealand," it said.

"Our country has a reputation for producing safe, high-quality food products which are in demand around the world, and this coward's letter doesn't change that at all.

"These letters are an attack on all New Zealanders, designed to gain publicity and cause the maximum damage to the New Zealand economy."

The threat, originally made in November, was to contaminate products unless 1080 was banned by the end of March.

Clement said a team of 36 officers had been investigating the threat since November and appealed for public assistance tracking down the blackmailer.