Finance Minister Grant Robertson spars with Steven Joyce over defence upgrade

A war of words has erupted between the new Finance Minister and the man he replaced, over whether enough money has been set aside for a big-ticket defence force upgrade.

The upgrade was announced last year, but the new Government says the money hasn't been put aside for it.

Finance Minister Grant Robertson says predecessor Steven Joyce failed to budget for the $20 billion needed for the upgrade, which could include buying Japanese military transport aircraft.

Mr Joyce disagrees, saying there's $110 billion of capital spending available until 2030, which Mr Robertson has called a "fantasy figure".

He insists that was a projection by Treasury and it fails to account for unforeseen spending on unpredictable events, such as earthquakes.