China expert Anne-Marie Brady says New Zealand must join Canada in applying pressure on China amid an escalating diplomatic feud between the two.

Canadian Prime Minister Justin Trudeau called New Zealand Prime Minister Jacinda Ardern on Monday in an attempt to shore up support for its condemnation of China's recent diplomatic actions.

The pair discussed the legal treatment and detention of Canadian citizens in China, and the extradition case of a Huawei executive in Canada, according to Trudeau's office.

Brady said Canada was contacting its allies for support, just as New Zealand would and had done in the past.

"United we stand, divided we fall. The New Zealand Government needs to stand with Canada on this issue. We need the support of our friends and allies too and we must uphold our values-based foreign policy," Brady told the Herald.

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"China should respect other nations' judicial procedure and rule of law, and it should not use foreign citizens as pawns."

Ardern was not available for comment today but a spokeswoman for duty minister Grant Robertson confirmed Ardern had a brief conversation with Trudeau yesterday.

"Although the cases are a consular matter between Canada and China, as the extradition case relates to a Huawei executive in Canada, there are principles at stake that concern us all."

The spokeswoman said the Government closely monitored international developments which may affect the safety of New Zealanders abroad but advice for travel to China was to exercise normal safety and security precautions.

Trudeau has suggested China used its judicial system to pressure Canada over the arrest of Meng Wanzhou, chief financial officer of Chinese telecommunications giant Huawei, who is also the daughter of Huawei's founder.

And, earlier this week, a Canadian citizen in China was sentenced to death after he was convicted of drug smuggling.

"I will say that it is of extreme concern to us as a government, as it should be to all our international friends and allies, that China has chosen to begin to arbitrarily apply the death penalty, as in this case, facing a Canadian," Trudeau told reporters on Monday.

Trudeau, who also spoke to Argentine President Mauricio Macri on Monday, has received support from allies including the US, the European Union, France, Germany, Britain and Australia.