Senior Donald Trump advisor Kellyanne Conway allegedly punched a man in the face at the President’s inauguration ball just hours after the Republican leader was sworn in, a witness has claimed.

Ms Conway reportedly stepped between two men who started fighting at the invite-only Liberty Ball on Friday.

When the scuffle continued, Mr Trump’s top adviser allegedly hit one of the men in the face with closed fists at least three times, a witness told New York Daily News.

The account was corroborated by Fox business correspondent Charles Gasparino who said Ms Conway was “throwing some mean punches.”

“Inside the ball we see a fight between two guys in tuxes and then suddenly out of nowhere came trump adviser Kellyanne Conway who began throwing some mean punches at one of the guys,” he wrote on Facebook.

“Whole thing lasted a few mins [sic] no one was hurt except maybe the dude she smacked. Now I know why trump hired her.”

The reports came as Ms Conway defended Sean Spicer’s false claim that the 45th President's inauguration audience was the “largest ever”, saying he had used “alternative facts”.

However, NBC's Meet the Press presenter Chuck Todd responded: "Alternative facts are not facts. They are falsehoods."

Mr Spicer had originally stated: “This was the largest audience to ever witness an inauguration -- period -- both in person and around the globe.”

Despite widespread debunking of the fictitious claim, Mr Spicer stood by the assertion on Monday saying: “It was the most-watched inaugural...There were tens of millions of people that watched that online … It’s unquestionable.

“I’d love to see any information that proves that otherwise. I don’t think there’s any question that it was the most-watched inauguration ever. I think I’m right in saying Reagan didn’t have YouTube."