23 year old video clip surfaces of more sexist Trump remarks while in NZ.

US Republican presidential candidate Donald Trump's comments about sexually assaulting women are "indefensible", says Prime Minister John Key.

Trump and Democratic rival Hillary Clinton faced-off at the second Presidential debate on Monday, after a torrid week of sparring that saw Trump hunkered down in his gilt Trump Tower, following the release of footage condemned by Republicans, his wife Melania and running mate Mike Pence alike.

Trump was forced to apologise after a previously unaired Access Hollywood tape caught him bragging about trying to have sex with married women and groping others without permission.

MIKE SEGAR/REUTERS US Republican presidential nominee Donald Trump.

After the debate, Key said the campaign had become intense, and mired in a "fair bit of controversy".

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"The comments themselves were indefensible, and that's why he's gone out and apologised for them.

RADIO NEW ZEALAND Donald Trump's campaign's in turmoil as he heads into the second presidential debate with Hillary Clinton this afternoon.

"I think all of us have got a chance to see Donald Trump, over the course of the last few months, realise that he's not a person who is prone to apologising very often. Clearly he, himself recognises that.

"Ultimately, whether he's fit to be the President of the United States, that's a matter for US voters I think."

Key would not be drawn on whether Trump's comments were "locker room banter", but said "that language is indefensible".

Key's comments also follow Newshub's unearthing of decades-old footage of Trump talking about his love of beautiful women while in New Zealand.

The US presidential candidate told his interviewer his views on women should prevent him from running for political office.

Trump was interviewed by TV3 (now Newshub) while visiting New Zealand in 1993 as part of a consortium bidding for a casino operator's licence. In the interview, Trump was asked about his image as a womanising tycoon.

Trump said: "I think women are beautiful – I think certain women are more beautiful than others, to be perfectly honest – and it's fortunate I don't have to run for political office."

​Newshub Political Editor Patrick Gower said he found the interview in TV3's archives.

"Donald Trump declared his sexist views on women would disqualify him from political office," said Gower. "Trump's comment now stands out as a blunt assessment of himself, with the continual exposure of his aggressive sexist attitude and actions now derailing his Presidential campaign."

Trump's presidential campaign is in disarray as he is engulfed in scandal over a leaked videotape.

In the 2005 tape Trump is heard discussing his attempts to bed a married woman, and bragging that he can "do anything" to women because he is a celebrity.

"When you're a star, they let you do it. Grab them by the p..... You can do anything," he says.