Hillary Clinton is on the cusp of a commanding presidential election victory over Donald Trump if the latest poll - 51-37 in the Democrat's favour - is to be believed.

The Associated Press-GfK poll gives the Democrat her largest lead yet with just 12 days until the election.

The poll showed Mrs Clinton has the support of 90 per cent of likely Democrat voters, and also has the backing of 15 per cent of more moderate Republicans. Just 79 per cent of all Republicans surveyed said they were voting for their party's nominee.

With voting already underway in 37 states, and Mrs Clinton leading in many of the key swing states, Mr Trump's opportunities to overtake his rival are quickly evaporating. However, a Fox News poll gave Mrs Clinton just a three-point lead, at 44-41.