Hillary Clinton is the most unpopular she's ever been, disliked by six out of ten voters, a poll showed Monday - and there could be worse to come for the candidate as the impact of the FBI's email bombshell becomes clearer.

The Democrat is seen unfavorably by 60 per cent of voters to Trump's 58 per cent, according to the ABC News/Washington Post tracking poll.

That is her worst showing since the survey began tracking in May last year, shortly after she announced her candidacy.

The survey was conducted from Oct. 27-29 - only partially after the FBI sensationally announced on Friday that it was investigating thousands of emails that might be related to the former secretary of state's private server.

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Clinton's campaign were left reeling Friday when the FBI revealed it was investigating thousands of emails that might be related to the former secretary of state's private server

Trump's campaign has seized on the revelations as further evidence that the Clinton dynasty cannot be trusted

The messages were taken as part of a separate FBI investigation into devices belonging to disgraced ex-congressman Anthony Weiner - the estranged husband of top Clinton aide Huma Abedin.

The former politician came under investigation after the DailyMail.com revealed he had exchanged lewd text messages with a 15-year-old girl.

Clinton and Trump are the most unpopular presidential candidates by far since the ABC/Washington Post poll began in 1984. The billionaire's unfavorability ratings reached a high of 70 per cent in mid-June.

The survey showed Clinton still holding the slimmest of leads over the Republican, at 46-45 per cent - within the margin of error of three points.

A Politico/Morning Consult poll showed Monday that she has a three point lead over Trump, in the first survey to be conducted entirely after the FBI's sensational news.

With just eight days until Nov. 8, the Democrat has 46 per cent of the vote against her rival's 43 per cent, the poll showed. Libertarian candidate Gary Johnson has seven per cent and Green Jill Stein has five.

Clinton and Huma Abedin earlier this month on her campaign plane. Abedin's husband Anthony Weiner came under investigation after the DailyMail.com revealed he had exchanged lewd text messages with a 15-year-old girl

The online survey, which has a margin of error of two points, was conducted over the weekend. Her three-point lead is the same as a poll conducted just before the revelations, Politico said.

Weiner, whose personal electronic devices were seized by the FBI, has an 8 per cent approval rating, making him somewhat less popular than Russia

Some 39 per cent of voters said the new email review would not sway which candidate they chose.

A third said it made them much less likely to vote for Clinton - albeit most of those were Trump voters in any case.

Among undecided voters, 42 per cent said they were less likely to vote for her - but 41 per cent said it would not make a difference to them.

Meanwhile Weiner himself has an 8 per cent approval rating, making him somewhat less popular than Russia.

At least 21 million people have already cast their votes, according to the New York Times. In some battleground states, including Florida and Colorado, almost a quarter of voters have already put in their ballots.

It emerged Sunday that the FBI now has a warrant to search the emails, numbering some 650,000 according to the Wall Street Journal.

Coming after weeks of emails published by WikiLeaks - which have given voters an unprecedented insight into a candidate's political machine - Trump's campaign has seized on the revelations as further evidence that the Clinton dynasty cannot be trusted.

'We never thought we were going to say "thank you" to Anthony Weiner!' Trump crowed to a Las Vegas crowd.

Forty-five per cent of respondents to the poll said they agreed with Trump's claim that Clinton's ongoing email scandal is 'worse than Watergate'.

Clinton and her campaign have demanded that the FBI give specifics on what exactly they are investigating, while several key Democrats have accused the organization of breaking the law by trying to sway the election.