New Zealand First leader Winston Peters has been condemned for "naked political opportunism" after he called for Muslim communities to "clean house" and turn in terrorists in the wake of the London attacks.

Peters made his comments in support of a Government motion to condemn the terror attack in London, and offer condolences and support to victims and the people of the United Kingdom.

They were immediately condemned by Act leader David Seymour, while United Future leader Peter Dunne warned against "the forces of bigotry and intolerance who will milk these events for every opportunity that they can".

Peters told Parliament there was a tendency to minimise terror attacks as the act of self-radicalised, lone wolves.

"That needs to be completely re-thought in the West...we must ask, 'how could people plan such terrible deeds but leave their friends, mothers, fathers, brothers, sisters and spouses completely in the dark?' Inevitably we will be told that the wider community knew nothing, and neither did friends or family," Peters said.

"What is happening is that family, friends and confidants are choosing to turn the other cheek, are choosing silence, rather than to turn these monsters in. That may be the culture of Damascus, but it is not ours. It may be acceptable in Tripoli, but it most certainly is not acceptable in New Zealand."

Peters said the "Islamic community" needed to "clean house" by "turning these monsters in".

"It starts with their own families. For New Zealand, we must avoid the same politically correct trap that has allowed such communities apart to form. That is, it is we who must change, they say, as a society to accommodate the cultural practices and traditions of others.

"No longer. We must stop the slide as a people, as a culture in the West...before we see in this country, in a New Zealand locality, a repeat of these events."

Speaking after Peters, Act leader David Seymour said such attacks were "getting increasingly close to New Zealand, both culturally and geographically".

"There is going to have to be a wider and more serious debate about when and whether such an event can happen here. It will have to be a debate without naked political opportunism as we have heard from New Zealand First, but also without the naivety that these events are completely random, that they are not systematic, and they cannot be detected and prevented."

United Future leader Peter Dunne said he extended his condolences to everyone affected by the attacks, and said the country needed to be on guard and that "we do not surrender".

"But equally that we do not surrender to the forces of bigotry and intolerance who will milk these events for every opportunity that they can. Our world faces a threat to its stability in a way that it has not known previously," Dunne said.

"People of good will and good spirit need to come together to work out sensible solutions to these problems - not revel in the pit of bigotry and intolerance, because all that does is intensify the hatred and give rise to the next event."

Over the weekend terrorists killed seven people and wounded 48 others by ramming a vehicle into a crowd on London Bridge and then stabbing people in nearby Borough Market.

In comments after the attack, British Prime Minister Theresa May warned there had been "far too much tolerance of extremism" in the UK, saying "enough is enough".

Labour leader Jeremy Corbyn said May had overseen as home secretary a 19,000 fall in police numbers. Asked if he agreed with calls by some for May to quit, Corbyn said he did but added the best way for the issue to be addressed was by voters in the election on Thursday UK-time.

More than 130 imams and Muslim religious leaders have said they will refuse to say funeral prayers for the perpetrators of the attack.