The US Supreme Court on Friday voted to end constitutional protections allowing the right to abortion that have been in place for almost 50 years, since the famous 1973 Roe v Wade decision.

The move, which was carried by five votes to four in America's highest court, is expected to lead to bans on abortion in about half the nation's 50 states.

Ms Ardern compared the move with New Zealand's 2020 decriminalisation of abortion.

"Watching the removal of a woman's fundamental right to make decisions over their own body is incredibly upsetting," she said in a statement on Saturday.

"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."

The Kiwi leader recognised people hold strong convictions on both sides of the abortion debate, but said those beliefs should not extend to preventing someone making a decision reflecting their own circumstances.

"To see that principle now lost in the United States feels like a loss for women everywhere," she said.

"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."

Australian Associated Press