A 60-year-old New Zealand businessman has been arrested over threats to contaminate infant formula with 1080 poison.

The Auckland man has been charged with two counts of blackmail, NZ Police Commissioner Mike Bush told a media conference.

He will appear in Manukau District Court on Tuesday afternoon.

The arrest comes after police executed five search warrants in Auckland and the Rangitikei district on Tuesday morning.

Anonymous letters were sent to Fonterra and Federated Farmers in November last year along with small packages of milk powder laced with a concentrated form of 1080.

They contained threats to contaminate infant and other formula with the poison unless New Zealand stopped using 1080 for pest control by the end of March.

More than 50,000 tests failed to reveal any contamination.