Trump campaign reiterates claims that US election is fixed

US Republican presidential candidate Donald Trump has intensified allegations that the upcoming election is being rigged in favour of his opponent Hillary Clinton, as he slips further behind the Democrat in a variety of polls.

Trump has fallen dramatically in surveys since a leaked tape showed him bragging about sexual assault in an interview with Access Hollywood presenter Billy Bush.

He accused Clinton and the US media of making a joint effort to scupper his campaign.

"The election is absolutely being rigged by the dishonest and distorted media pushing Crooked Hillary - but also at many polling places - SAD," Trump tweeted on Sunday evening.

At a campaign rally in New Hampshire on Saturday Trump also told his supporters that the election was rigged.

"Remember, it's a rigged system. It's a rigged election," he claimed.

The latest poll from NBC News/Wall Street Journal showed an 11-point lead for Clinton ahead of the third and final televised debate in Las Vegas this Wednesday.

Former GOP House of Representatives Speaker Newt Gingrich also attacked the role of the media in the election thus far, telling ABC News that it had waged an "unending one-sided assault" against the New York businessman.

In response to the allegations from Trump and Gingrich, Democrat vice-presidential candidate Tim Kaine referred to them as "wild, kind of scorched-earth tactics".

The US presidential election takes place on November 8.