Donald Trump was given a dressing down during a rare, unannounced campaign stop to grab some food and meet the press at a burger bar in Manchester, New Hampshire, when a passing customer shouted he was a racist.

"Enjoy your burger, racist!" the heckler told the property tycoon as he gave an on-camera interview before adding "I love New Hampshire." ABC interviewed the woman, who identified herself only as Jane from South Carolina and declined to give her second name.

"I'm really struck by his racism and Islamophobia," she told the station. "I wanted to make sure people remembered that he is racist, and that he's using it to rally voters." Jane added she felt if she had remained silent she would be giving her tacit approval to the Republican frontrunner who has divided public opinion with his remarks.

Trump, who is leading national polls for the republican nomination, has sparked controversy for his comments on immigration, particularly for saying the US should introduce a ban on all Muslims entering the US in the wake of an Islamic State (Isis)-inspired mass shooting in Santa Barbara.

"Until we are able to determine and understand this problem and the dangerous threat it poses, our country cannot be the victims of horrendous attacks by people that believe only in Jihad, and have no sense of reason or respect for human life," Trump said following the attacks.

The reality TV star also stoked controversy for his comments on Latin American immigration. One of his key policy commitments is a pledge to build a wall along the United States' southern border with Mexico.

"[Mexico] are sending people that have lots of problems, and they are bringing those problems to us. They are bringing drugs, and bringing crime, and they're rapists," he claimed.

Trump has denied accusations of stoking racial hatred. Immediately after his anti-Muslim comments, Trump claimed "I am the least racist person that you have ever met" in one interview.