New Zealand voiced concern over the barring of the four MPs, who visited as part of a cross-party delegation, noting its lawmakers have paid visits to Taiwan for decades.

But Beijing's embassy in Wellington said the delegation had defied repeated warnings in travelling to the self-ruled island, where they met with Vice President Hsiao Bi-khim.

"The actions of these MPs violate the one-China principle and constitute interference in China's internal affairs," an embassy spokesperson said, referring to Beijing's position that it is the sole legitimate government of China, including Taiwan.

"Whoever crosses the red line on the Taiwan question will face the consequences," the spokesperson added.

China claims self-ruled Taiwan is part of its territory and opposes the democratic island's participation in international organisations and exchanges with other countries.

New Zealand Foreign Minister Winston Peters's office denied the visit violated his government's position on the status of the island democracy.

He defended the MPs' right to visit Taiwan and said he had instructed the nation's diplomats "to express concern at this departure from past practice and to better understand it".

"New Zealand Members of Parliament are free to make their own individual decisions, independent of the government, about how they respond to invitations to travel overseas," his spokesperson said.

While Wellington does not have diplomatic relations with Taiwan, "this does not preclude New Zealand from maintaining trade, economic, cultural and indigenous exchanges", the foreign ministry said.

"We intend to continue these exchanges as they benefit the people of New Zealand and are entirely consistent with our One China policy."

Australia's Foreign Minister Penny Wong told a hearing of the country's Senate that Canberra was "concerned" by the bans and diplomats would raise the issue with Chinese counterparts.

Taiwan's foreign ministry said it "strongly condemns" the ban, insisting "China has no right to interfere" in its international interactions.

- 'Disappointing' -

New Zealand lawmakers Simon O'Connor and Ingrid Leary created the All-Party Parliamentary Group on Taiwan in March 2023 with the goal of improving ties with the island and holding discussions about trade, healthcare and semiconductor technology.

The Chinese embassy in Wellington raised immediate concerns about their visits.

Taiwan's foreign affairs ministry said last month the trip was the group's third since its founding.

One of the MPs hit with a ban, Laura McClure, told RNZ that China was trying to intimidate New Zealand lawmakers.

"New Zealand is sovereign, and members of parliament have the right to represent the communities and constituents that we do, and we have the right to travel freely around the globe," she said. "That is part of living in a free democracy."

RNZ reported that the Chinese embassy in Wellington had said it would reverse the ban if the politicians apologised.

"It's not exactly clear what we would be apologising for, and if it is just for travelling to Taiwan, I personally will not be apologising," McClure said.

Beijing's foreign ministry defended the ban as lawful and urged the lawmakers "to earnestly respect China's sovereignty and territorial integrity".

"Crossing the line or overstepping the boundary on the Taiwan question will inevitably come at a price," ministry spokesperson Mao Ning told a news conference on Thursday.

Labour MP Duncan Webb, who took part in the trip, told RNZ that the lawmakers had been warned by the Chinese embassy before travelling that they faced a ban if they went.

"With the increasing tensions I suppose a response wasn't surprising, but I think it is disappointing," he said.