Joe Biden has promised supporters "we're going to win this", as the race for the White House remains on a knife edge.
Addressing the Americans at a drive-in rally he likely hoped would have been the site of a victory speech in Delaware, the Democrat challenger said people should "keep the faith" while vote counting continues.
"It may take a little longer," he warned, after crucial swing states he hoped to flip like Arizona, Georgia and North Carolina went down to the wire, remaining too close to call.
And others he wanted to turn blue - Michigan and Pennsylvania - face severe reporting delays, with no official result likely this morning.
"We're gonna have to be patient, until the hard work of tallying votes is finished," Mr Biden said, in a speech that lasted only a few minutes, adding: "It ain't over 'til every ballot is counted."
A bullish Donald Trump tweeted in response from the White House where he is watching the results unfold: "We are up BIG, but they are trying to STEAL the Election.
"We will never let them do it. Votes cannot be cast after the Poles [sic] are closed!"
Mr Biden's campaign told NBC the race for the White House remains a "slog", as the margin between him and Mr Trump is very close.
They are still "confident" of winning enough crucial battleground states to hit the 270 Electoral College votes needed to clinch the presidency.
But they concede hopes for a convincing victory that could have been celebrated on election night are unlikely to be realised.
While the results have not yet been officially announced, a Sky News/ NBC projection shows Mr Trump is on course to hold on to Ohio, Florida, Iowa and Texas.
