New Zealand Prime Minister John Key has become the latest target in the white powder scare that has hit several senior politicians and the French embassy.

Police say a postal worker sorting mail in Mr Key's west Auckland electorate of Kumeu noticed white powder leaking from an envelope early on Tuesday.

The Fire Service hazardous materials unit was called in to decontaminate the scene and testing is being carried out to determine what the substance is, police spokeswoman Beth Bates said.

It's the seventh white powder scare in recent days.

Similar packages have also been sent to Earthquake Recovery Minister Gerry Brownlee's office in the Beehive, independent MP Peter Dunne's Ohariu electorate office in Johnsonville, and ACT leader John Banks' Epsom electorate office.

The substance in these cases was found to be baking powder.

Envelopes were also sent to the ministry of health and the French embassy, and one turned up in Greymouth.

Four of the envelopes were sent from Waikato on the same day and had similar handwriting.

Police have yet to say whether they are all from the same source.