US President-elect Joe Biden's top coronavirus advisers have warned that President Donald Trump's stalling of the transition could hinder the country's pandemic response, as Trump and his allies persisted in challenging the November 3 election results.
Trump's refusal to concede has put Biden's transition to the White House in limbo, complicating his efforts to tackle a COVID-19 pandemic that has killed more than 247,000 people in the United States and shows no sign of slowing.
In a call with reporters, former US surgeon-general Vivek Murthy, who co-chairs Biden's COVID-19 task force, said blocking Biden transition advisers from meeting with government experts could harm their ability to confront the pandemic next year.
Several doctors and nurses associations published a letter on Tuesday urging the Trump administration to share critical COVID-19 data, such as equipment inventories, medical supplies and hospital bed capacity, with Biden's team.
Biden, a Democratic former vice-president who will take office on January 20, has also not been able to receive the classified intelligence briefings usually afforded a president-elect.
He met instead with his own panel of national security experts such as former Deputy Secretary of State Antony Blinken, former deputy national security adviser Avril Haines and former US Ambassador to the United Nations Samantha Power.
Trump, a Republican, has repeatedly claimed without evidence he is the victim of widespread voter fraud and his campaign has filed a flurry of lawsuits in battleground states. Election officials in both parties have said they see no evidence of serious irregularities.
Trump on Tuesday fired top US cybersecurity official Chris Krebs, who heads the Department of Homeland Security's Cybersecurity and Infrastructure Security Agency, accusing him without evidence of making a "highly inaccurate" statement that affirmed the security of the US election.
Biden won the national popular vote by more than 5.6 million votes, or 3.6 percentage points, with some ballots still being counted. In the state-by-state electoral college that determines the winner, Biden has secured 306 votes to Trump's 232.
In Michigan, where Biden leads by more than 145,000 votes, two Republican members of the board of canvassers in the state's largest county, Wayne, initially voted on Tuesday to stop the county certifying its results, citing slight inconsistencies in precinct totals in the majority-black city of Detroit.
But they reversed their decision after more than two hours of angry public comment, with the caveat the Michigan secretary of state conduct an audit of precinct tallies.
At a federal court hearing in Pennsylvania on Tuesday, US District Judge Matthew Brann appeared sceptical of Trump's request to block officials from certifying Biden's win in that state.
Trump supporters are also clinging to hope that recounts could reverse state results.
Georgia is undertaking a manual recount on its own. In Wisconsin, the Trump campaign has until Wednesday to decide if it will pay the $US7.9 million ($A10.8 million) a recount would cost there.
Biden on Tuesday spoke to Israeli Prime Minister Benjamin Netanyahu, a Trump ally, as well as the leaders of India, South Africa and Chile. Biden said he had spoken to 13 foreign heads of state thus far, telling them: "America's back. And it's no longer America alone."
He also filled several top positions in his White House. Campaign manager Jen O'Malley Dillon will serve as deputy chief of staff in the Biden administration.
Longtime advisers Mike Donilon and Steve Ricchetti will join as senior adviser to the president and counsellor to the president, respectively. Dana Remus, the campaign's top lawyer, will be counsel to the president.
Another close adviser, Ron Klain, was already named chief of staff.
Australian Associated Press