US Democratic presidential front-runner Hillary Clinton's once double-digit lead over rival Donald Trump has narrowed to just 3 points in a new poll.

According to the NBC News/Wall Street Journal poll released early Sunday, the former secretary of state leads the presumptive Republican presidential nominee 46 to 43 percent in a test matchup between the two likely nominees.

Clinton held an 11-point lead over Trump, 50 to 39 percent, in a similar poll conducted in April.

Democratic White House contender Bernie Sanders, however, is still holding a double-digit lead over the New York businessman in a hypothetical match-up, 54 to 39 percent, according to the Wall Street Journal/NBC News poll

Meanwhile, a majority of Americans view both Clinton and Trump unfavorably. Fifty-eight percent voters dislike Trump, while 54 percent have a negative opinion of Clinton, the poll found.

Forty-seven percent of voters said they would consider a third-party candidate if Clinton and Trump face off as the Democratic and Republican nominees in November, according to the survey.

In an interview earlier in the day, Sanders said Trump and Clinton are both “very strongly disliked” by the American people.

Sanders said one of the reasons he is staying in the race for the White House is because he does not want Americans to vote "for the lesser of two evils."

Sanders, 74, has long argued that although he is losing the primary presidential race to Clinton, Democratic Party officials should consider how well he does with independents as one of the reasons he is better prepared to compete against Trump in the general election.

An NBC News tracking poll also found last week that Clinton’s margin over Trump was narrowed from 5 points to 3 points.

Even though Trump and Clinton are gearing up for the general election, they still need to amass the required number of delegates to secure their respective nominations.

Clinton needs an additional 90 delegates to reach the required 2,383 to secure the nomination. Trump needs 1,237 delegates to clinch the nomination. AP estimates that he currently has 1,160.