Washington : US Democratic presidential candidate Hillary Clinton has a 12-point lead over her rival Republican Donald Trump and has reached 50 per cent support nationally among likely voters, a new  tracking poll shows.

The poll shows Clinton with 50 per cent support to Trump's 38 per cent, with 5 per cent backing Libertarian Gary Johnson and 2 per cent supporting the Green Party's Jill Stein.

The poll comes on the heels of the third presidential debate, which a post-debate CNN/ORC snap poll showed Clinton won.

The ABC News survey's results show Clinton with a 20-point advantage among women, and a three-point edge with men -- a group that has tilted toward Trump for most of the 2016 race.

Clinton leads among voters of all education levels -- but her three-point advantage with those without college degrees is smaller than her 20-point lead among voters with college degrees.

Trump's strongest group remains white, non-college educated voters, who back him 55 per cent to 36 per cent.

The ABC News poll was conducted October 20-22 and includes 874 likely voters. Its margin of error is plus or minus 3.5 percentage points.