Labour leader Jacinda Ardern's commitment to decriminalise abortion has already sparked controversy.

In the Newshub leaders' debate last night she said she would remove abortion from the Crimes Act if she was prime minister.

"It shouldn't be in the Crimes Act," she said during the debate. "People need to be able to make their own decision."

This morning on the AM Show she said it would be a conscience vote, where MPs could vote based on their views rather than along party lines.

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She expected some of those within her own caucus would also oppose the bill, but thought "there will be a majority of Parliament that think, actually in 2017, women shouldn't face being criminals for accessing their own rights".

"That doesn't mean it wouldn't have regulation that sits around it but we just don't think it should be in the Crimes Act."

Prime Minister Bill English, who is a devout Catholic, said he believed the country's abortion laws were working fine and the law should not be changed.

Abortions were currently only permitted as a medical procedure when the prospective mother faced serious physical or mental harm as a result of carrying the child to term and where two certifying consultants agreed. This meant many women and doctors had to lie to get the procedure performed.

The Abortion Law Reform Association of New Zealand welcomed Ardern's announcement.

National president Terry Bellamak said New Zealanders had waited 40 years to hear a leader on the threshold of the Prime Minister's office acknowledge our abortion bureaucracy is not fit for purpose.

"Our laws breach people's human rights by forcing them to lie to get the health care they need," she said.

"Ardern is right. Those who oppose abortion are free not to choose it. Those who need abortion should be able to access it freely, without having to get the approval of two certifying consultants."

But Family First NZ spokeswoman Marina Young opposed the announcement and said the existing safeguards protected both women and children.

"Any changes would potentially pave the way for late term abortions, aborting children on the basis of their gender, aborting those with disabilities e.g. Down syndrome, and possibly even partial-birth abortions," she said.

"If Labour is really concerned about women, they should be calling for a law which protects informed consent, that requires honest information about abortion and abortion-related risks, and that provides women with independent pregnancy counselling so that women can make truly informed decisions from a place of certainty and knowledge."

She said women who were getting abortions under the current guidelines were not committing an illegal act and were not considered criminals so there was no need for change.

This is not the first time a law reform on the issue has been proposed.

In 2010 Labour MP Steve Chadwick proposed a new law making abortion legal on request for women up to 24 weeks into their pregnancy but the Labour party stayed silent on the issue and the proposal did not proceed.