United States Supreme Court judge Ruth Bader Ginsburg's joke about moving to New Zealand if Donald Trump becomes US president may be raising chuckles here and all over social media, but the comment has landed her in hot water with the US legal fraternity.

The outspoken 83-year-old judge joked in an interview with the New York Times at the weekend that if Trump becomes president after the November elections, he might have to fill more than just the vacant Supreme Court seat of judge Antonin Scalia, who died in February at the age of 79.

She told the paper at the weekend: "I can't imagine what this place would be - I can't imagine what the country would be - with Donald Trump as our president.

"For the country, it could be four years. For the court, it could be - I don't even want to contemplate that."


She said then that the dilemma reminded her of something her husband, Martin D. Ginsburg, a prominent tax lawyer who died in 2010, would have said.

"'Now it's time for us to move to New Zealand,'" Justice Ginsburg told journalist Adam Liptak, smiling ruefully.

Ginsburg's joke has made waves around the world and on social media, raising chuckles from the most serious political commentators on the Washington Beltway to the most frivolous.

The judge is known for pushing the bounds of a justice's public comments, which has earned her something of a cult following on the left.

But legal experts say she just went too far this time, crossing a very important line in American jurisprudence, reports America's traditional paper of record, the Washington Post.

"I find it baffling actually that she says these things," Arthur Hellman, a law professor at the University of Pittsburgh, told the newspaper.

"She must know that she shouldn't be. However tempted she might be, she shouldn't be doing it."

It's a political cliche in America to joke about moving to another country if a certain presidential candidate does or doesn't win.

The paper said many Americans were headed to Canada if George W. Bush was re-elected in 2004. A similar contingent threatened to flood north when Barack Obama was elected and re-elected.

It said, though, that you generally don't hear a US Supreme Court judge talking like this.

"In fact, you generally don't hear a Supreme Court judge talking at all - much less about the big political issues of the day."

Political analyst and author Jeff Greenfield, who appears regularly on ABC, CNN and CBS news, went as far as demanding to know why Ginsburg does not recuse herself from the bench over her Trump comments.

Greenfield notes that Ginsburg was a part of the court that decided who the president would be when the 2000 election was thrown to the Supreme Court, saying that this is definitely not uncharted territory.

Had she said something similar about either Bush or Al Gore, would she have been able to hear the case?

Ed Whelan, president of the Ethics and Public Policy Center, and once the clerk for the late conservative judge Scalia, has criticised Ginsburg before for her public comments.

But he said this comment was more indefensible than any of her previous utterances.

"I think this exceeds the others in terms of her indiscretions," Whelan said.

"I am not aware of any justice ever expressing views on the merits or demerits of a presidential candidate in the midst of the campaign. I am not a fan of Donald Trump's at all. But the soundness or unsoundness of her concerns about Donald Trump has no bearing on whether it was proper for her to say what she said."

University of California law professor Rick Hasen said it's valid to question how Ginsburg might have to handle a potential Trump case - up to and including a Clinton v Trump case.

"I think this is ultimately a question for judicial ethicists, but I do think following these comments it is a legitimate question to raise, should Donald Trump's campaign come to the Court with any legal questions before the election," he said on his blog.

Earlier Huffington Post founder Arianna Huffington tweeted:

Kiwis responded positively, saying the country would welcome her if she really wanted to move here, and migrants to New Zealand pointed out that it was a great destination to move to, not just when times are bad elsewhere.

Grist, an online news outfit which uses humour to tackle green issues and inspire environmental action, invited all Americans terrified of Trump to move here.