The advice Julia Gillard has for US presidential hopeful Hillary Clinton

Julia Gillard has some advice for Hillary Clinton if she becomes the United States' first female president - call out any sexism early.

The former Australian prime minister gave Ms Clinton the free advice during a talk at Fortune magazine's Most Powerful Women summit in London on Monday night (Tuesday morning AEST).

Ms Gillard was asked on stage what guidance she had for the US politician - who is again running for president after an unsuccessful bid in 2008 - given the sexism she herself experienced in office.

The 53-year-old began by admitting she was "absolutely wrong" to think the maximum reaction to her being Australia's first female prime minister would come during the initial months in the job.

In fact as politically controversial issues arose down the track "the reaction about gender heightened because it became a sort of convenient cudgel of criticism when you wanted to take a shot at the government", she said.

"So in retrospect - and I think Hillary actually did this last time in the primaries with President Obama - if anything happens that's sexist you've got to call it out early rather than thinking it will all normalise itself, it will just go away by itself."

Ms Gillard said otherwise it became harder to later distinguish between normal political controversy and "this gendered bit".

She also told the summit that sexism wasn't an Australian issue.

To avoid putting baggage on female leaders everyone needed to shed the stereotype that "likeability and women and leadership don't go together", she said.

"This is not an Australian question this is a global question.

"We'll see some of it in real time I think during Hillary Clinton's campaign and this is the moment for us to be having these deep conversations about how to change it so that for the daughters in the future there's none of that baggage."