New Zealand Prime Minister John Key is not worried about the release of Nicky Hager's book, an investigative journalist who wrote about New Zealand's political fall-out ahead of the 2002 election and the National Party's strategy.

Mr Key told media he was not at all concerned about the book's release despite the fact that it might contain more intelligence leaks from Edward Snowden. The prime minister said whatever leaks were published, he didn't think they would be "embarrassing."

He said he would be surprised if people will still be shocked about New Zealand's intelligence agencies if they were indeed included in Hager's book. Mr Key declared "Nickey Hager is a screaming left-wing conspiracy theorist."

The prime minister thought the book was scheduled for release ahead of the September election to "maximise sales."

Hager's new book, Dirty Politics, will reportedly contain leaked emails between right-wing bloggers and National Party personalities. According to Hager, the book will tell the story of how "dirty politics" is out to "poison New Zealand's political environment."

Hager had accused the Prime Minister office of working with National Party "proxies" to carry out attacks to preserve Mr Key's reputation. A report by the Herald said the book is said to contain the email exchange between Whaleoil blogger Cameron Slater and Jason Ede, one of Mr Key's press secretaries, about Labour's website.

The book details the alleged discussion of Slater and Ede including information on how not to be caught in the act. In an interview, Hager said Mr Key will have some "serious" questions to answer.

Despite intensifying political campaigns ahead of the election, public support for Mr Key and the National party has increased in the recent polls. According to the polls, only 8 per cent prefer Labour Party leader David Cunliffe as the next prime minister while 28 per cent expressed their support for Labour.

However, the prime minister had downplayed National's lead in the polls and said he has no plans of being complacent. Mr Key told TV One in an interview that the poll results were "good" for National. He believes National has a long way to go between now and the election date.