Reports of bug sweeping, unusual burglaries and car tampering have prompted a call for the New Zealand government to defend academics from Chinese interference.

However, Prime Minister Jacinda Ardern says she wants evidence before taking action.

Since rising to prominence with a 2017 report critical of China's alleged influence in New Zealand, University of Canterbury professor Anne-Marie Brady says she has been subjected to attempts to silence her through pressure on organisations at home and abroad.

In February this year, she told an Australian parliamentary committee her office and home had been burgled, noting laptops - including one used for her work - had been taken but other valuables left untouched.

Police in September confirmed there was an ongoing, unusually long and well-resourced probe into the break-ins, with Interpol called in, and the NZ Herald reported spies had been called to search Prof Brady's office.

This month, the researcher raised suspicions her car had been tampered with.

The reports have prompted dozens of academics and human rights advocates to call for the government to take a stand and for authorities to treat the claims more seriously.

"We have been shocked and disturbed by the reports of intimidation and harassment suffered by (Prof Brady) ... Academics must be able to work without fear," a group of 29 said in an open letter on Monday.

"We also urge Prime Minister Jacinda Ardern to make a clear statement in defence of academic freedom in New Zealand ... and to be very clear that any intimidation and threats aimed at silencing academic voices in this country will not be tolerated."

Ardern told reporters on Monday she would respond if she had proof.

"If I received a direct report that said there was an issue there that could be directly attributable to China, or at China's direction, we would act on that. But I have not received such information," she said.

"I absolutely defend the right of academics to utilise their academic freedom ... They should continued to be able to do their work with freedom from repercussion from this government or any other government."

The country's centre-right National Party and Ardern's Labour Party have played down suggestions of political interference by China in recent years, saying the country's donation and electoral system are up to scratch and authorities are vigilant.

In a testimony earlier this year to the US-China Economic and Security Review Commission, former CIA China expert Peter Mattis accused New Zealand politicians of not doing enough about Chinese political influence.