There is no reason to believe there aren't potential terrorists living in New Zealand, Winston Peters says as he calls for Muslims to "clean house" and speak up.

The New Zealand First leader's comments on the AM Show echoed those he made in Parliament on Tuesday where he urged Islamic communities to turn in those who may pose a threat to the country and it "should start with their own families".

Mr Peters used the recent terror attacks in London and Manchester as an example of communities "turning the other cheek rather than turning these people in".

"When you have people saying these people are lone wolves, they always say these people are unhinged, and the third thing they always say - 'we didn't know about it' - what? The whole family, every friend of a certain group didn't know about this?

"One of those people, the first one they caught in the London case, authorities they knew about him, but they didn't know enough. If five or six people close to him had have alerted them, there would have been a red alert," Mr Peters told the AM Show on Wednesday.

In 2015, the Government said there were around 40 people on the terror watchlist who were being monitored 24 hours a day, many of whom were suspected of raising money for Islamic State.

"That's a massive amount of resources going into looking into certain people who may be a worry to us. This is a fact and when I hear Muslims say that to me, then I kind of think I should take it seriously."

Asked whether he believed New Zealand could be harbouring potential terrorists, he replied: "Why would we be exempt?"

He also called for tougher vetting for those looking to live in New Zealand.

"I would ensure anyone coming here as an immigrant or refugee, they're properly and thoroughly investigated as to their background.

"I'd do the job properly, and make sure I knew who was coming and whether or not they were prepared to, whatever our flag is, respect it, whatever our values might be, respect them and understand we're a country of tolerance and freedom."

Mr Peters' comments in Parliament on Tuesday faced criticism for being an opportunist.

"There will have to be a more serious and wider debate about when and whether such an event can happen here," ACT Party leader David Seymour said.

"And it will have to be a debate without naked political opportunism, as we have heard from New Zealand First."

United Future leader Peter Dunne, who has previously warned against racial intolerance, said there were those who would use bigotry and intolerance "for every opportunity they can get".

Newshub.