The Reserve Bank conveniently breaks this down by institutional ownership from which you can spot the buyers and sellers.
An obvious seller is the Earthquake Commission fund, which has offloaded over $2 billion of its NZ government bond portfolio since 2010 while still holding just over $1.7 billion of the stuff as at June 2012.
Notable buyers of NZ government securities since 2010 include non-resident institutions (doubling up to $28.4 billion over the period) and NZ registered banks, loading up from $12.5 billion in 2010 to almost $18 billion as at this June.
Another group of keen buyers of NZ government debt include "trustee and nominee companies", which have increased holdings from $7.8 billion in 2010 to current levels of $13.3 billion. This is probably the influence of KiwiSaver funds, and looking at the longer time series, the rise in holdings by this sector does appear to mirror the lifeline of the scheme.
At any rate the New Zealand Debt Management Office (NZDMO) hasn't had any trouble hocking off bonds and whatnot. The latest NZDMO data shows it has raised about $7 billion from investors so far this calendar year at much reduced interest rates compared to a few years ago.
For instance, at the latest bond auction we borrowed $100 million due in April 2015 at an effective interest rate of 2.67 per cent and $150 million (due in 2023) at 3.57 per cent. In August 2011 both the medium- and long-term NZ government bond rates were over 6 per cent.
A good time to borrow more, you might think, but instead the NZDMO told us in May it would wind down on the credit card.
Government borrowing, the NZDMO statement says, "... will be reduced by $3 billion over the forecast period ending June 2016, relative to plans outlined by the NZDMO at the Pre-election Economic and Fiscal Update (PREFU) in October 2011."