Photo taken on July 14, 2020 shows the U.S. Supreme Court building in Washington, D.C., the United States. (Xinhua/Liu Jie)

US President Donald Trump said Tuesday he will announce his pick on Saturday for the crucial Supreme Court seat left open by the death of justice Ruth Bader Ginsburg - and his Republican Party vowed a quick vote to confirm the nominee.

US Democratic opponents, led by presidential candidate Joe Biden, have demanded that Republicans back off on replacing Ginsburg - who died last week - until after the November 3 election, when they'll know whether Trump is getting a second term.

Republicans are ignoring this, giving Trump, who has already replaced two other justices, a chance to tilt the nation's highest court to the right for decades to come, whether he beats Biden or not.

Speaking at a campaign rally in Moon Township, Pennsylvania, Trump said he would reveal his nominee at 5 pm (2100 GMT) on Saturday at the White House.

"We're going to pick a great woman," he said to chants of "Fill that seat!" from the crowd. "We have great support from the Republican Party."

Trump indicated he would hold off on announcing his choice until the end of the week out of respect for the memorial services for Ginsburg taking place in the capital.

He has pledged to choose a woman for the lifetime post.

Leaders of the Republican majority in the Senate, which is tasked with confirming court nominees, said they have enough support to hold a vote on the nomination either before the election or at worst during the "lame-duck" session between the election and the inauguration of the next president in January.

"We will certainly do that this year," Republican Senate leader Mitch McConnell said.

Although two Republican senators said they believed the upper chamber of Congress should not vote at all before the election, the party's 53-47 majority is still just big enough to go ahead.

One of the other key potential Republican holdouts, frequent Trump critic Mitt Romney, said Tuesday he would move ahead with the process.

"If the nominee reaches the Senate floor, I intend to vote based upon their qualifications," Romney said.

Trump welcomed what he called a "very positive statement" by Romney, who was the only Republican senator to vote for impeaching the president.

Democrats argue that any Senate vote should be delayed until after the election has made clear who will lead the country from 2021.

AFP