Joe Biden has again said he is confident of victory as he inches closer to beating Donald Trump after Tuesday's US presidential election.
The Democratic challenger now has 253 of the 270 Electoral College votes needed to clinch the White House under the state-by-state US voting system.
Mr Biden leads vote counts in the battlegrounds of Georgia, Nevada, Pennsylvania and Arizona.
A Biden win would see Mr Trump leave office in January after four years.
As counting enters its fifth day, it is still unclear when the contest will end.
Officials are tallying up record numbers of postal votes due to the coronavirus pandemic, causing the longest delay to a presidential election result in 20 years.
What did Biden say?
"We're going to win this race," Mr Biden told supporters in Wilmington, Delaware, on Friday night, striking a confident tone. He was joined by his running mate, California Senator Kamala Harris.
He said he was on track to win more than 300 Electoral College votes and pointed out that more people had voted for his campaign - over 74 million people - than any US presidential candidate in history.
Mr Biden said Americans had given him a mandate to tackle the coronavirus pandemic, the struggling economy, climate change and systemic racism. On Friday for the third straight day the US set a fresh record for new Covid-19 cases, with more than 127,000 infections.
The Democrat - presenting himself as the candidate of unity after a bitterly fought campaign - said it was time to "get the vitriol out of our politics" and "be civil to one another".
"We may be opponents but we're not enemies, we're Americans," said Mr Biden, who did not mention his Republican opponent, Mr Trump.
Mr Biden's appearance had originally been planned as a victory speech, but he opted instead to give a general update on the state of the race as US TV networks cautiously held off declaring him the winner.
The Democrat said he hoped to address the nation again on Saturday.
'A holding speech rather than a victory speech'
Joe Biden delivered a holding speech rather than a victory speech, but he hit all the familiar themes that will no doubt feature if and when he addresses the nation as president-elect.
He's been remarkably consistent throughout the campaign - that's part of his appeal in these chaotic times. He hailed the election results so far as a broad mandate for change, although they're not the resounding repudiation of President Trump for which the Democrats had hoped. Once again he presented himself as a leader who believes in America, who could unify the bitterly divided country - "the purpose of politics isn't total unrelenting warfare" he said.
In the same breath he nodded to his own impatience for an outcome, and presented a stark contrast to President Trump's false claims of voter fraud. Watching the ballot tallies is "slow and numbing" he said, but they represent people who "exercise the fundamental right to have their voices heard."
What happens next?
Mr Biden - who ran twice previously for the White House, in 1988 and 2008, without success - would be the oldest president ever inaugurated at 78.
If he is declared the victor this weekend, his team is expected to begin its transition process on Monday. The New York Times reports Mr Biden could announce the first senior officials in his potential administration as early as next week.
The Secret Service has sent reinforcements to Delaware to beef up Mr Biden's security detail. The Federal Aviation Administration has restricted flights over Wilmington's airspace.
However, there is no indication Mr Trump will concede to his opponent in the short term.
"Joe Biden should not wrongfully claim the office of the President," he tweeted on Friday afternoon. "I could make that claim also. Legal proceedings are just now beginning!"
Mr Trump has been making unsubstantiated claims of election fraud, spurring some fellow Republicans to speak up that the rhetoric should be toned down.
Since at least 1896 every defeated presidential candidate has conceded defeat to the winner. But there is no law or constitutional requirement to do so.
The constitution does however state that a new elected president will automatically take office at noon on 20 January following an election.
What's the mood inside the White House?
President Trump is angry and disappointed that more of his allies are not rallying to his side on television or in the streets, according to White House officials on Friday.
On Saturday he wrote a series of tweets making unsubstantiated allegations of illegality in the voting process - all of which were labelled as disputed and potentially misleading by Twitter. He also insisted he had won the election "by a lot".
He has been watching television, making phone calls to on-the-ground campaign offices, and dividing his time between the Oval Office and the residence.
Several aides did not show up for work on Friday and the White House was described as "very empty" with a sombre mood.
Adding to the bad news, it was reported on Friday night that White House Chief of Staff Mark Meadows, 61, had tested positive for coronavirus.
The president has indicated to senior advisers that he will forge ahead with legal challenges to the results, although there is still no firm strategy for such litigation.
One senior outside adviser to the president described his mood on Friday as "somewhere between sullen and hopeful". The source added that Mr Trump "was the last one to think he could win in 2016", despite his top aides telling him that he would.
What's the current state of the race?
Mr Biden is leading Mr Trump by more than 4 million votes out of a record 145 million cast. But US presidential election results are decided on a state-by-state basis in the Electoral College, and the contest is much closer in the key battlegrounds.
Mr Biden has 253 Electoral College votes, while Mr Trump has 214. To win the White House, a candidate needs 270.
In Pennsylvania, where Mr Biden was born, he is ahead by nearly 29,000 votes, with 99% counted. If he takes that state along with its 20 Electoral College votes, he will win the election.
Officials released a statement on Friday saying that the "overwhelming majority" of postal and absentee votes had now been tallied, and they were now beginning to count provisional ballots. However they did not say when the count will be complete.
The Rust Belt state voted Democratic in six consecutive White House races before it swung to Mr Trump in 2016.
In Georgia, Mr Biden is currently leading with more than 7,000 votes, and 99% of the ballots counted. Georgia's secretary of state said there would be a recount because the margin was so small.
Georgia (16 electoral votes) is a traditionally Republican state and has not been won by a Democrat in a presidential race since 1992.
Mr Biden leads by more than 22,000 votes in Nevada (six electoral votes) and by fewer than 30,000 in Arizona (11 electoral votes).
Mr Trump leads in North Carolina (15 electoral votes) by more than 76,000 ballots.