Government figures which show foreigners bought five times as much precious New Zealand land last year are not an accurate guide to foreign ownership, Land Information Minister Mark Mitchell says.

Mitchell rejected any claims that there was "a big buy-up of New Zealand land" today and ruled out calls for a detailed register which showed every foreign purchase, not just the sensitive or large purchases approved by the Overseas Investment Office (OIO).

The OIO said 466,000 hectares of land was sold to offshore buyers in 2016 - five times more than the previous year.

But Mitchell told TVNZ's Q+A this morning that the figure could be misinterpreted because some of that land was jointly bought by New Zealand investors.

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Net sales of New Zealand land had been consistent over the last decade, he said.

Mitchell was also challenged on how much it knew about the scale of foreign investment in New Zealand.

He said Statistics New Zealand was developing a process to capture more information about foreign investment.

"It's getting better and better. And in terms of the OIO, we are able to monitor and watch very carefully, in terms of the applications that are coming through the office."

He added: "I think it's really important to note that when we're talking about offshore investment and overseas capital ... is that we have got a very extremely robust process that they have to go through before that actually gets signed off."

The minister did not any express interest in a register - an initiative which New Zealand First leader Winston Peters has been lobbying for.

A private member's bill in Peters' name which would have created a register was voted down last year.

Peters said today that there was no official record of New Zealand land and houses bought by foreigners, as there was in other countries.

New Zealanders would be "alarmed" by how much was being bought offshore, he said.

Peters also questioned whether the OIO followed up on conditions imposed on foreign investors.

In order to gain approval from the OIO, investors often promise to create jobs, recreational opportunities, or carry out conservation initiatives on the land.

Mitchell said the OIO used a combination of public tip-offs and proactive enforcement to check whether conditions were being met.

He said there had been several breaches of conditions by investors, but he could not give a precise figure.

Land Information NZ began keeping records of the number of houses being bought by offshore tax residents in 2015. Around 2 to 3 per cent of New Zealand houses are being sold to non-residents, the records show.

However, it is not considered a register of foreign ownership because it counts corporations and trusts as NZ residents. It also counts students and temporary workers as residents, even if they do not intend to stay in the country.