Most young Americans do not view Donald Trump as a legitimate president, according to a new poll.

The 45th president of the US has not been embraced by the country's youth, a GenForward poll found, with 57% of people aged 18-30 viewing Trump's presidency as illegitimate, the Associated Press reported.

The poll also found about three quarters of black and Latino people surveyed by GenForward did not believe the president was legitimate, while 53% of white people polled did believe Trump was a legitimate president.

Just 22% of those aged 18-30 approved of President Trump, while 62% disapprove of the Republican.

The president's overall popularity rating has also fallen since his inauguration, with a recent survey, by Fox News, finding 51% of people polled disapprove of the president, while 43% of people approve.

This is a drop of five points from the same survey taken just one month ago, with the breakdown of disapproval ratings showing Trump's decisions on immigration and healthcare and the US's relationship with Russia all apparent bones of contention for voters.

Trump has had a challenging first month in office, which was marred by forced resignations, inconsistent statements from various members of his team, numerous leaks from within the White House, and subsequent allegations that members of Trump's team had contact with Russian figures prior to his inauguration.

And a separate poll taken a week earlier, by CNN/ORC, showed Melania Trump's approval rating had overtaken her husband's.