Democratic presidential candidate Hillary Clinton has opened up a yawning 23-percentage-point lead over Donald Trump with female voters, according to the latest national poll.

It's the third major poll in days that has revealed a widening gap between Trump and Clinton, with the Democratic candidate pulling ahead.

The latest poll, by ABC News and the Washington Post, finds Clinton ahead of Trump among all registered voters by eight points (50% to 42%), which is double the lead the Democrat held on the eve of the Republican National Convention. The poll was conducted the first four days of August.

Clinton is particularly popular among all categories of women, according to the poll, with a 58% to 35% lead, the highest of the campaign to date. She is 19% ahead of Trump among white, college-educated women, who were evenly split between the candidates just last month. She also currently leads Trump by 6% among all college-educated white voters, which Democrats haven't won in exit polls since 1976.

Clinton enjoys a huge lead among all non-white voters with 75% support to Trump's 18%, the poll finds, with 92% support among blacks for Clinton to 2% for Trump, and 69% Hispanic support for Clinton to 26% for Trump.

Clinton is now also supported by 86% of voters who backed Bernie Sanders in the primary, and has the support of most Catholics in the nation, which is a key swing vote.

Clinton is backed by 92% of mainline Democrats, and Trump only by 83% of mainline Republicans.

But Trump far out surpasses Clinton in his bedrock support group of non-college educated white men — a massive 67% to Clinton's 27%. He's also resoundingly supported by conservatives with 73% to 21% for Clinton, and by evangelical white Protestants (76% to 18%).

The poll found that Trump has a host of negatives to overcome if he's to make up any ground. Of those surveyed, 79% of Americans say he doesn't show enough respect for people he disagrees with, 70% express anxiety about a Trump presidency, 67% think he lacks the temperament to serve effectively, 64% question his understanding of world affairs, 62% say he's not trustworthy and 61% think he's unqualified for office.

Voters aren't happy with Trump's attack on the US Muslim family who lost a son fighting for America in Iraq, with 73% of voters disapproving of his behaviour, including 59% of Republicans.

But Clinton has her own negatives to overcome. The poll found that 66% of those surveyed believe she's too willing to bend the rules (though this is an improvement over the previous month), and only 38% believe she is honest and trustworthy. But among those surveyed 61% believe she had the personality and temperament to be president, and 72% believe she understands international affairs.

When the first post-convention poll numbers emerged, Trump said it was still "very, very early."