Prime Minister John Key says he won't lose any sleep over losing $5 million on the National Business Review's Rich List for 2012.

Key is on the verge of falling off this year's list after his estimated fortune fell from $55m to $50m. At 157th place he ranks last and is just on the threshold for inclusion.

However, the prime minister today questioned the accuracy of the list.

''That is the magic of the people that put together those lists,'' he told Radio Live.

''I don't know where they got it from a year ago and I don't know where it's gone this time. I think they interview their own typewriter when they put that list together.''

Key laughed off suggestions his reported fall in wealth made him look like a poor fiscal manager.

"How would you know how they got the numbers in the first place. So no, I'm losing any sleep on that.''

Key first made the Rich List in 2008 with an estimated fortune of $50m. Last year he also rejected the accuracy of the annual list as "made up by a bunch of journalists".

Because of his political position, Key's money is invested for him in a blind trust, meaning he doesn't actually know where it is held so cannot be accused of political interference to line his own pocket.

The NBR uses valuations of listed shares, sales of private companies and other valuation techniques to estimate the wealth of those it ranks.

For the first time ever a non-New Zealander has topped the list. Auckland business tycoon Graeme Hart, worth $6 billion, has been surpassed by Russian steel magnate Alexander Abramov, who is valued at $7b.

Abramov is building a $40m luxury waterfront home in the Bay of Islands.

- © Fairfax NZ News