Democrat Hillary Clinton has a five percentage point lead over Republican Donald Trump in the US presidential race, according to the latest Reuters/Ipsos opinion poll, roughly the same advantage she has held all month.

The survey result out on Friday showed little movement following Monday night's presidential debate, the first of three debates before the November 8 election.

The September 23-29 national tracking poll showed that likely voters support Clinton over Trump by 43 per cent to 38 per cent, while another 19 per cent said they would not pick either candidate.

Clinton has mostly led Trump in the poll this year, and her level of support has been for to five percentage points higher than Trump's in each of the last four weeks.

Among likely voters, 42 per cent supported Clinton, 38 per cent supported Trump, seven per cent supported Libertarian candidate Gary Johnson and three per cent supported Jill Stein of the Green Party.

Monday's debate was the most watched presidential debate in US history, with an estimated 84 million people tuning in for the 90-minute exchange.

Some 56 per cent of Americans adults who watched the debate said Clinton won, according to a Reuters/Ipsos poll released on Wednesday.
Voters appeared to be warming up to both candidates in Friday's poll.

Some 48 per cent of likely voters said they had an overall favorable view of Clinton, compared with 45 per cent in the previous week, while 46 per cent said they had a favourable view of Trump, up from 44 per cent the week before.

Some polls, like Reuters/Ipsos, try to include only likely voters, while others include all registered voters.

The Reuters/Ipsos tracking poll also gathers responses every day and reports results twice a week, so it often detects trends in sentiment before most other polls.

An average of major opinion polls aggregated by RealClearPolitics showed Clinton ahead of Trump by 2.9 percentage points on Friday, or 47.3 points to 44.4, slightly lower than the previous margin of three points on Wednesday, but well up from 0.9 point on September 19.