Biden says Trump's failure to concede is an 'embarrassment'

US President-elect Joe Biden has insisted that nothing would stop the transfer of power and said it was an "embarrassment" that President Donald Trump has not conceded the election.

Trump is pursuing lawsuits in several states in a long-shot bid to hold on to power. His campaign said it would file a lawsuit to stop Michigan from officially certifying Biden as the winner there until the state could verify that votes were cast lawfully, the latest in a flurry of lawsuits in battleground states to try to back up Trump's unsupported claims of widespread fraud.

Legal experts have said Trump's litigation has little chance of changing the outcome, and state officials have said there were no significant irregularities in the November 3 election.

Meanwhile, Trump supporters faced a possible setback in Pennsylvania. A witness who had raised accusations of ballot tampering recanted his allegations, according to Democrats in Congress who were briefed on the investigation.

Trump's accusations of fraud did not appear to be gaining traction with the public. Nearly 80 per cent of Americans, including more than half of Republicans, recognise Biden as the winner, according to a Reuters/Ipsos poll.

Top Republicans in Congress, including Senate Republican Leader Mitch McConnell, said Trump had a right to challenge Biden's victory, and others echoed the president's unfounded accusations of widespread fraud. Privately, some aides said Trump would need to produce credible evidence soon to retain their support.

Biden secured more than the 270 votes in the Electoral College needed to take the presidency by winning Pennsylvania on Saturday after four tense days of counting, which was delayed by a surge in mail-in ballots due to the coronavirus pandemic.

Biden said in a speech in Delaware that his team was pushing ahead with forming a new administration to take over on Inauguration Day, January 20, 2021, no matter what.

"We're going to be going, moving along, in a consistent manner, putting together our administration, the White House, and reviewing who we're going to pick for the Cabinet positions, and nothing's going to stop that," he said on Tuesday. 

Taking questions from the media for the first time since his victory, Biden was asked what he would say if Trump were watching. He said: "Mr. President, I look forward to speaking with you."

US Secretary of State Mike Pompeo predicted a "second Trump administration," in comments at odds with congratulatory phone calls from the leaders of Britain, France, Germany and Ireland to Biden.

Trump installed loyalists in top positions at the Pentagon, one day after firing Defence Secretary Mark Esper, which could potentially make it easier to use US troops to respond to domestic protests.

The Biden transition team has been unable to move into federal government office space or tap funds to hire staff because a Trump appointee who heads the federal office charged with recognising election results has not yet done so.

"The whole Republican Party has been put in a position with a few notable exceptions of being mildly intimidated by the sitting president," said Biden, who chuckled when asked about the Pompeo remarks.

British Prime Minister Boris Johnson, a conservative whose blustery style is often likened to Trump's, said he spoke to Biden on Tuesday by phone about working together on priorities like climate change, promoting democracy and recovering from the pandemic.

Turkish President Tayyip Erdogan also congratulated Biden, a former vice president now heading to take over the White House after almost five decades in politics.