Trump one of most incompetent US presidents: Joe Biden

President-elect Joe Biden has said President Donald Trump was the "most incompetent" presidents in US history.

Sidestepping the questions related to impeachment or removal from office in the remaining 12 days, Biden said that quickest way Trump could be removed is his inauguration on January 20.

"I have been saying for now well over a year he (Trump) is not fit to serve," Biden said. "He is one of the most incompetent presidents in the history of the United States of America and so the idea that I think he shouldn't be out of office yesterday is not the issue."

"The question is what happens with 14 days left to go or 13 days left to go and I think that what 81 million people stood up and said it is time for him to go and the United States Senate voted 93-6 to confirm that we should be sworn in. We were duly elected, so I think it is important we get on with the business of getting him out of office," Biden told reporters in Wilmington in Delaware.

"The quickest way that that will happen is us being sworn in on the 20th. What action happens before or after that is a judgment for the Congress to make, but that is what I am looking forward to, him leaving office," the president-elect said.

Biden said Trump had clearly demonstrated and exceeded "even my worst notions" about him.

"He has been an embarrassment to the country, embarrassed us around the world, not worthy, not worthy to hold that office," Biden said.

"If we were six months out, we should be moving everything to get him out of office, impeaching him again, trying to invoke the 25th Amendment whatever it took to get him out of office. But I am focused now on us taking control as president and vice president on the 20th and to get our agenda moving as quickly as we can," Biden said.

Asked about Trump not attending the inauguration, Biden said this was one of the few things that the two had ever agreed on.

"It's a good thing him not showing up," Biden told reporters.

The president-elect, however, said outgoing Vice President Mike Pence was welcome to attend the inauguration on January.

"I think it is important that as much as we can stick to what have been historical precedents of how and the circumstance in which an administration changes should be maintained and so if Mike --if the vice president is welcome to, I would be honoured to have him there and to move forward in the transition," Biden said.

Responding to a question, Biden said that he has not spoken to Pence.