Prime Minister John Key has accused the Labour Party of "backing rapists" in an extraordinary attack in Parliament this afternoon.

That came after Labour MP Kelvin Davis shouted at Mr Key on the way into the House, accusing him of inaction in helping New Zealand detainees in Australia.

"Prime Minister, you're gutless," Mr Davis yelled as Mr Key walked past.

The Labour MP was pushed aside by Mr Key's security staff.

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The heated debate on New Zealanders detained on Christmas Island continued inside the House.

Under questioning by Labour leader Andrew Little, Mr Key went on a furious offensive.

In an angry attack, he said: "Some of the [detainees] are rapists, some of them are child molesters, and some of them are murderers.

"These are the people that the Labour Party are saying are more important to support than New Zealanders who deserve protecting when they come back here.

"Mr Davis, if you want to put yourself on the side of sex offenders, go ahead my son, but we'll defend New Zealanders."

Labour MPs yelled that Mr Key had "lost the plot".

When Mr Little questioned why New Zealand did not demand more action from Australia, Mr Key launched another attack.

"You back the rapists," the Prime Minister said, before being cut off by the Speaker.

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That prompted a heated debate across the House.

Labour MP Iain Lees-Galloway was thrown out of the debating chamber after criticising the Speaker.

Labour MPs then staged a walk-out in protest at Mr Key's comments. Just three Labour women remained in the House.

Labour MPs staged a walk-out in protest at John Key's comments. Just three Labour women remained in the House.
Labour MPs staged a walk-out in protest at John Key's comments. Just three Labour women remained in the House.

Mr Robertson, making a point of order, said he was "deeply offended" and asked that Mr Key withdraw his comment.

Speaker David Carter said the comment could stand.

"It is not a matter of whether the member was offended, it is a matter of whether the House was offended," he said.

That prompted further objections from Labour's whip Chris Hipkins and Green Party co-leader Metiria Turei.

"This is nothing more offensive than being accused of backing rapists," Mr Hipkins said.

Mr Carter refused to back down and make Mr Key withdraw the comment.

The Prime Minister said that in discussions with his Australian Prime Minister Malcolm Turnbull, his counterpart had told him that rapists and murderers were among the people who were going to be deported.

At the end of Parliamentary question time, the Labour Party sought leave for vote of no confidence in the Speaker.

National MPs refused to grant leave.

Outside Parliament, Mr Little told reporters Mr Key had "lost his moral compass".

Asked about Mr Key's outburst, the Labour leader said the Prime Minister "knows he is on the back foot" on the Christmas Island crisis and his only response was to "lash out in a nasty, vicious way".

He said the detainees at the offshore facility had been convicted of "petty" offences like shop-lifting and driving offences.

Mr Little defended Mr Davis' heckling of the Prime Minister outside the debating chamber.

He said the MP, who visited Christmas Island two weeks ago, had been taking "distressing" phone calls from the detention centre and he "wants the Prime Minister to know about it".

Mr Davis said he believed his heckling had prompted Mr Key's angry response in the House.

"I would say that's what's rattled him," he told the Herald.

Mrs Turei said Mr Key's comments on rapists were a "huge misjudgement" that appeared to show he was "losing it".

She said his "weird outburst" was deeply offensive, especially for women MPs who had worked on tackling sexual and family violence.

United Future leader Peter Dunne said Mr Key's comments were "unfortunate" and had inflamed an already tense situation.

"I don't think this was robust [debate] today. I think this was one of the more despicable question times."

Mr Dunne said the Speaker should have intervened. But he said he would not have supported a no confidence motion because it was a "stunt" by Labour.

He also said he was uneasy about New Zealand's response to the detainee situation on Christmas Island, saying the Government appeared to have been caught "flat-footed".