Far-right activist Richard Spencer has been punched during an interview with the ABC at an anti-Trump protest in Washington DC.

Mr Spencer, president of the white nationalist National Policy Institute, was talking to ABC Washington bureau chief Zoe Daniel when a masked man lunged at him, landing a blow to the right side of his face.

Members of the crowd were accusing Mr Spencer of being a "neo-Nazi" when the attack happened.

"Neo-Nazis don't love me, they kind of hate me actually," Mr Spencer said during a confrontation.

From the left side of the camera the attacker throws a punch that hit Mr Spencer flush on the right cheek, sending him reeling backwards.

His attacker then ran off.

Sorry, this video has expired The first day of President Donald Trump

Punch was second attack on Spencer

Daniel said it was the second time Mr Spencer had been punched by the same man.

"I moved across to ask him what he was doing at the protest and to get his reaction to being punched by a random stranger," she said.

"It was during that conversation that the masked man came back again, running from a distance to deliver a much harder blow to the head.

"Activists and protesters who were also throwing questions at Mr Spencer ran after the assailant while we went and asked him if he was alright."

Mr Spencer took to Twitter to assure his follower he is "OK" after the attack.

"I think I probably did suffer some kind of like a mild concussion or something because my brain feels a little scrambled to be honest," he said in a Periscope video.

Spencer's rise as alt-right personality

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The National Policy Institute is a US think tank that is part of the alt-right movement, and became infamous after members shouted "Heil Trump!" during a conference in Washington last November.

Mr Spencer himself was filmed shouting "Heil Trump, heil our people, heil victory!", while some at the meeting lifted their hands in a Nazi salute.

The non-profit Southern Poverty Law Centre, which tracks hate groups, has described Mr Spencer as an "academic racist" who backs creation of an Aryan homeland.

Twitter suspended several accounts linked to the alt-right following Mr Trump's election, including Mr Spencer's, which has since been reinstated.