National and Labour are toeing the one-China line, but ACT leader David Seymour says he would be happy to visit Taiwan if invited.

China's diplomats have been using fiery language and not-so-veiled threats in response to US Speaker of the House Nancy Pelosi's visit to Taiwan.

Pelosi has been travelling around Asia and while her stop in Taiwan is not considered official she was greeted by the island's foreign minister and has been exclaiming US solidarity, saying the world faces a choice "between autocracy and democracy".

China's military was put on high alert, and the defence ministry said it would launch "targeted military operations" in response to her visit.

"These moves, like playing with fire, are extremely dangerous. Those who play with fire will perish by it," China's foreign ministry said in a statement.

"The United States, for its part, has been attempting to use Taiwan to contain China. It constantly distorts, obscures and hollows out the one-China principle, steps up its official exchanges with Taiwan, and emboldens 'Taiwan independence' separatist activities.

"China will definitely take all necessary measures to resolutely safeguard its sovereignty and territorial integrity in response to the US Speaker's visit. All the consequences arising therefrom must be borne by the US side and the 'Taiwan independence' separatist forces."

New Zealand's Prime Minister Jacinda Ardern told media this afternoon the government's stance had not changed.

Prime Minister and Labour leader Jacinda Ardern. Photo: RNZ / Angus Dreaver

"There have been visits by MPs over the years, but the last visit at a ministerial level I believe was in about 1998. New Zealand does engage with Chinese Taipei economically through APEC and that's long been our tradition," she said.

"None of these actions change the position that we have. We have long been a nation that in the face of tensions like these that we'll call for dialogue. I'm pleased to see that both presidents from China and the United States have recently had lengthy calls. That is positive. Dialogue and diplomacy is what we need in these tense times."

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However, she stopped short of criticising Pelosi's visit.

"It's not for New Zealand or for me to cast judgement on the decisions from other leaders as to where they visit and why. What New Zealand will keep calling for though is ongoing diplomacy and dialogue to overcome what are tensions, particularly around the Taiwan Strait."

Opposition leader Christopher Luxon struck much the same tone, even voicing specific support for the one-China policy and saying he would not visit Taiwan as prime minister if National won power.

"Like all western countries we have a one-China policy, we want to uphold that," he said.

He said Pelosi's visit was ultimately a decision for the US.

"From our perspective we'll be watching that closely. We really want the US and China to resolve its own tensions and we want to be able to work with both countries."

ACT's leader David Seymour also said Pelosi's visit was a US domestic decision, "but I would say that any person has the right to go to [capital city] Taipei if the people of Taipei want them there".

"It's not up to the CCP to decide who can go to Taipei," he said. "The fact that they even think that's an acceptable position shows we've got problems."

He said he had never been to Taiwan, but would visit if invited. Whether that would lead to a diplomatic incident is uncertain.

China's Ambassador to New Zealand was, however, repeating his government's condemnation of Pelosi's visit, which he described as a "major political provocation to upgrade US official exchanges with Taiwan".

"The one-China principle is the overwhelming consensus of the international community, the political foundation for China's relations with other countries, the essence of China's core interests, and a red line and bottom line that cannot be touched or crossed," he said in a letter.

"Some US politicians are flagrantly playing with fire on the Taiwan question for selfish gains. The US side has shown the world what a bully it is. This will only make people of all countries see more clearly that the United States is the biggest destroyer of peace today."

China maintains that Taiwan is an inalienable part of its territory in what is known as the one-China policy.

"This has been clearly recognised by United Nations General Assembly Resolution 2758 of 1971," the foreign ministry said.

"Since the founding of the People's Republic of China in 1949, 181 countries have established diplomatic relations with China on the basis of the one-China principle. The one-China principle is a universal consensus of the international community and a basic norm in international relations."

While the densely populated group of islands was recognised as a country by the United Nations between 1949 and 1971, it is now classified by the UN as a territory - and all but 13 countries officially hold to the one-China doctrine.