White House counsel Pat Cipollone took the floor for opening arguments at an extraordinary weekend session of the 100-member Senate, which will decide whether the 45th US president should be removed from office.

Democratic prosecutors from the House of Representatives, which impeached Trump on December 18, wrapped up their detailed case for the president's removal late Friday over his dealings with Ukraine.

Cipollone said the House prosecutors had not made their case.

"We don't believe that they have come anywhere close to meeting their burden for what they're asking you to do," he said. "In fact, we believe when you hear the facts... you will find that the president did absolutely nothing wrong."

The White House counsel said Democrats were asking the Senate to "overturn the results of the last election."

"They're asking you to tear up all of the ballots across this country on your own initiative," he said. "Take that decision away from the American people."

Trump's lawyers will have 24 hours spread over three days to present their defense of the president to the Senate, where Republicans hold a 53 to 47 seat majority.

They plan to speak for up to three hours on Saturday and resume their presentation on Monday.