Most Americans view Donald Trump and Hillary Clinton unfavorably: Suffolk University/USA Today poll

US Republican presidential nominee Donald Trump (right) and his Democratic rival, Hillary Clinton

A majority of Americans hold an unfavorable view of Republican presidential nominee Donald Trump and his Democratic rival, Hillary Clinton, and consider them untrustworthy, a new poll shows.

According to the Suffolk University/USA Today poll, released on Thursday, the former secretary of state is viewed negatively by 51 percent of voters and the New York billionaire by 59 percent. About 20 percent of likely voters say they don't like either major-party nominee.

A third-party candidate who is certified on a majority of state ballots should be included in the presidential debates, 76 percent of voters say, according to the survey.

Clinton leads Trump by 7 points in the run-up to the 2016 US presidential race. She is favored by 48 percent of likely voters to Trump’s 41 percent. Another 9 percent are undecided.

Clinton received 42 percent to Trump’s 35 percent in a four-candidate match-up. In that scenario, Libertarian presidential nominee Gary Johnson earned 9 percent, while Green Party candidate Jill Stein bagged 4 percent.

The Suffolk poll was conducted from August 24 to 29 among a national sample of 1,000 likely voters. The margin of error is 3 points.

The former First Lady leads the billionaire among women, 54 percent to 38 percent; among black voters, 92 percent to 4 percent; and among Hispanic voters, 65 percent to 24 percent.

Clinton has led Trump throughout most of the 2016 presidential campaign. But her latest lead represents a stronger level of support than polls showed in recent editions of the poll. But recent polls have shown Trump gaining ground on Clinton.

Clinton has a 4.9-point lead over Trump, 46.8 percent to 41.9 percent, the RealClearPolitics average of polls showed.

The Fox News poll, released on Wednesday, showed that Trump reached within 2 percent of his Clinton. The Democratic nominee was leading the businessman 41 percent to 39 percent.

Libertarian presidential candidate Gary Johnson (AFP photo)

US Green Party presidential nominee Jill Stein (AFP photo)

Johnson scored a healthy 9 percent and Stein took 4 points.

The poll attributed the former secretary of state’s declining support to Johnson and Stein’s growing popularity among voters which had mostly happened at the expense of Clinton.