Deputy Prime Minister Winston Peters has issued a new warning over alleged Chinese spying in New Zealand.

It comes after a University of Canterbury professor had her home and office broken into a number of times after claiming China has been "undermining the integrity of the New Zealand political system ".

"You'd be terribly naïve to think that New Zealand citizens are not being spied on by foreign powers," Mr Peters told RadioLIVE.

"It's been going on for decades but the issue in this case is from whence it's happening."

Someone who has been investigated is National Party MP Dr Jian Yang.

Dr Yang came under scrutiny after Newsroom alleged he had studied and taught at a spy school before moving to New Zealand. He admitted teaching students English to help them with their spying activities.

Mr Peters says he's "concerned" about Mr Yang's alleged activities, which reportedly led to a Security Intelligence Service investigation into his background.

"The reality here is that we're being asked to believe that someone who was part of the Chinese secret service has no longer any loyalty to that service," he says.

"And I don't hear enough denials, I don't hear statements."

Mr Yang has denied ever being a spy and says there was no basis to the allegations against him.

"I refute any allegations that question my loyalty to New Zealand," he said in a media statement at the time.

"I challenge those who are propagating these defamatory statements to front up and prove them."

But Mr Peters says Mr Yang's failure to take legal action over the allegations against him is concerning.

"Those allegations are massively defamatory, but no one's suing, are they?" he asks.

"If they're not true, they're awfully defamatory, so why has there not been a lawsuit about that matter?"

Newshub.