Defence Minister Gerry Brownlee called on China to explain its island building programme in the South China Sea.
The sea - one of the world's main trade routes - is a source of major geopolitical tension.
China claims more than 80 percent of the waters, and in recent years has built artificial islands with airstrips and stepped up its military presence. This has angered many southeast Asian nations which have competing territorial claims.
Fresh from returning from the Shangri-La security forum in Singapore, Gerry Brownlee said the pace of China's land reclamation in the South China Sea was spooking some nations.
He said China's artificial islands now covered more than 3000 acres of new land, on top of the atolls that were already there.
"The world hasn't really dealt with that type of thing before. While there's always been reclaim from the existing land out into the sea, that's something we all understand. To create a new space in a sea, and then with all the consequences for territorial sea, economic zone etc., it's somewhat new," Mr Brownlee said.
The South China Sea disputes are pressing, as an international arbitration court in The Hague prepares to rule on a case brought by the Philippines against China, with regards to its territorial claims.
The ruling is expected in the coming weeks and China has already said it won't recognise it.
Mr Brownlee said New Zealand was not taking sides, but it would support the international rule of law.
He said he had told his Chinese counterpart it was extremely important that communication lines, sea lanes and skies remained open in the South China Sea.
"The relationship between New Zealand and China is a strong one, it's quite robust and we can discuss problems that others see, like that, and encourage a particular solution."
Mr Brownlee's comments were spot on, said the Labour Party's foreign affairs spokesperson David Shearer.
"China's expansion of the Spratly Islands and the Paracel islands, have created a lot of nervousness amongst countries that neighbour those islands and obviously they're in dispute.
"It's difficult to see how they could be in any way full of the ambit of civilian use as China claims."
Mr Shearer said if the international ruling came out in the Philippines' favour, it would create some real issues.
Victoria University professor of strategic studies Robert Ayson said the timing of Mr Brownlee's comments was interesting, especially ahead of the international ruling.
"There will be few surprises about what New Zealand's position is likely to be there, which will be one that asks countries to take heed of the tribunal's ruling.
"The timing's also interesting in terms of the forthcoming New Zealand Defence White Paper, where I think the language on the South China Sea and China's actions there is going to be stronger than it was six years ago."
The Defence White Paper was due to be finished last year but, after delays, is expected to be released this month.
It sets out the capabilities of the Defence Force and the international environment it operates in.
Dr Ayson said there was a growing chorus of countries expressing concern at what was happening in the South China Sea.
"It's one thing for traditional partners to have these concerns... it's another thing when partners in the region who are much closer to the action have concerns, and are willing to say things."
"Singapore and Indonesia have been willing to say things in the last year or two that they probably wouldn't have said before. So there is a growing chorus that New Zealand wishes to be part of," Dr Ayson said.