A 78-year-old white man accused of punching a black protester in the face during a rally in North Carolina for Republican presidential candidate Donald Trump has been arrested on an assault charge.

Rakeem Jones, 26, was being escorted from the rally on Wednesday night by sheriff's deputies in Fayetteville when John Franklin McGraw hit him, the Cumberland County Sheriff's Office said in a statement.

Video of the incident recorded by bystanders showed deputies pinning Jones to the ground, prompting criticism on social media about why swift action was taken against him instead of his assailant.

"He had no right to put his hands on me," Jones said in a telephone interview.

The sheriff's office said it would conduct an internal investigation, adding that the deputies accompanying Jones did not see the assault.

Sheriff Earl "Moose" Butler called the attack cowardly and unprovoked. It was not immediately known if McGraw, who is charged with assault and disorderly conduct, had a lawyer.

"Regardless of political affiliation, speech, race, national origin, colour, gender, bad reputation, prior acts or political demonstration, no other citizen has the right to assault another person or to act in such a way as this defendant did," Butler said.

Trump's campaign rallies are boisterous, with the billionaire businessman often pausing to scold protesters and ask security officers to take them away. At a rally last month in Nevada, he said of a protester: "I'd like to punch him in the face."

The New York real estate magnate is the front-runner to be his party's nominee for the Nov. 8 presidential election.

Trump's hour-long speech in the packed North Carolina arena was interrupted at least 16 times, according to a Reuters reporter who attended.

A friend of Jones, Ronnie C. Rouse, said they attended the event to observe, not protest, and were told to leave after an exchange with another man who Rouse said used a racial slur.