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Millions of American women have lost the constitutional right to abortion, after the 50-year-old Roe v Wade decision protecting the right to an abortion was overturned.
Ardern said in a statement today that the decision was a loss for women everywhere.
"Watching the removal of a woman's fundamental right to make decisions over their own body is incredibly upsetting," she said.
"Here in New Zealand we recently legislated to decriminalise abortion and treat it as a health rather than criminal issue.
"That change was grounded in the fundamental belief that it's a woman's right to choose. People are absolutely entitled to have deeply held convictions on this issue. But those personal beliefs should never rob another from making their own decisions.
"To see that principle now lost in the United States feels like a loss for women everywhere.
"When there are so many issues to tackle, so many challenges that face women and girls, we need progress, not to fight the same fights and move backwards."
Foreign Affairs Minister Nanaia Mahuta tweeted that it was "draconian" and does not support women's right to choose.
Green Party MP Chlöe Swarbrick blasted the decision, expressing "solidarity with Americans fighting for restoration of their rights to healthcare."
ACT leader David Seymour said that "It may be that this is just returning the question to a state one, but half the states are going back a century in just a few days."
Green Party MP Jan Logie does not expect the decision will encourage people to push for changes to the abortion laws in New Zealand.
Logie said she is grateful New Zealand decriminalised abortion in 2020.
"We've seen a result of that an increasing number of New Zealanders who recognise the importance of reproductive justice. But this tells us also that we cannot be complacent."
Logie said she fears the decision will increase the rate of unsafe abortions in the US.
National Party leader Christopher Luxon has not made any public statements on the decision yet.
He previously has said he is against abortion personally, but not interested in changing New Zealand law.