New Zealand's reluctance to publicly back Canada over its dispute with China has raised questions about its commitment to the Five Eyes.

Canadian Prime Minister Justin Trudeau personally called Prime Minister Jacinda Ardern in January to discuss the legal treatment and detention of Canadian citizens in China, according to Trudeau's office.

But the New Zealand Government has been notably quiet in its response, with the Ministry of Foreign Affairs and Trade saying it was a "consular matter between Canada and China".

"New Zealand and Canada have discussed the detention and legal treatment of Canadian citizens in China, and the need for all countries to respect judicial procedure and rule of law," a spokesperson told CBC News.

Trudeau's phone call to Ardern related to Canada's relationship with China which deteriorated badly at the end of last year after Meng Wanzhou, the daughter of Huawei's founder, was detained in Vancouver in December.

Two Canadian men were arrested in China after Meng's arrest in Canada, and Trudeau reached out to several leaders to condemn the retaliation, according to CBC News reporter Evan Dyer who obtained the memorandums.

Australia did not immediately offer support for Canada. But after an open letter was published by more than 30 Australian academics calling for the government to respond, Foreign Minister Marise Payne expressed "concern" over the detentions.