Donald Trump has jumped ahead of Hillary Clinton by 4 percentage points, the first time he has led her in a national poll since 38 days ago.

The poll of 1,000 likely voters from Rasmussen Reports found that 43 per cent would vote for Trump if the November election were held today, compared with 39 per cent for Clinton.

That represents a 9-point swing in just the last week: Seven days ago the same pollsters reported that Clinton was leading the presidential race by 5 points.

I'M WINNING: Donald Trump will soon be crowing about a new Rasmussen Reports poll that has him leading Hillary Clinton by 4 percentage points nationally

WE SHALL OVERCOMB: Clinton has led Trump in every other poll since mid-May

The last time Trump polled better than her in a national survey was a May 22 survey from ABC News and the Washington Post that had him up by 2 – a lead smaller than the poll's margin of error.

'It remains to be seen whether he’s just having a good week or this actually represents a real move forward among voters,' Rasmussen reported online.

Part of that good week was a widely praised speech in western Pennsylvania about trade, and a stunning vote among United Kingdom citizens to leave the European Union – a move that resonated with Trump supporters.

Trump is gaining ground among younger voters, at least among Rasmussen's sample of Americans: While other polls show Clinton with sizable leads in that group, Thursday's release shows the two candidates tied among voters under 40 years of age.

Another source of Trump's apparent momentum is an advantage over Clinton among crossover defectors who plan to vote against their own party registration.

The billionaire Republican has cornered 14 per cent of the Democratic vote, according to Rasmussen, while the former Democratic secretary of state has only attracted the support of 10 per cent of Republicans.

He also leads among independent voters, by a sizable 18-point margin.

But another 28 per cent of likely voters without a party affiliation aren't choosing either of the two front-runners. Some are undecided, while others say they will support a third-party candidate.

Rasmussen's question read: 'If the 2016 presidential election were held today, would you vote for Republican Donald Trump or Democrat Hillary Clinton?'

The resulting numbers have a margin of error of 3 percentage points.