Joe Biden was last night on the brink of winning the race for the White House as Donald Trump mounted legal challenges in a bid to stop votes being counted in key battle states.
"After a long night of counting, it's clear that we're winning enough states to reach 270 electoral votes," Mr Biden said.
"I'm not here to declare that we've won, but I am here to report that when the count is finished, we believe we will be the winners."
Margins remained tight in several fiercely contested states including Michigan, Pennsylvania and Wisconsin, where Trump has already called for a recount.
His campaign team also launched legal challenges against postal votes in Pennsylvania and over claims they had not been allowed to observe the opening of ballots in Michigan.
However, Joe Biden last night addressed the American people and said he now expected to win the White House along with running mate Kamala Harris.
"I will govern as an American president," he said. "There will be no red states and blue states when we win, just the United States."
After the victory in Wisconsin, he held 248 Electoral College votes, 22 shy of the 270 needed to win the presidency.
Trump campaign manager Bill Stepien said the president would formally request a Wisconsin recount, citing "irregularities" in several counties.
The campaign said it was filing suit in Michigan and Pennsylvania to halt ballot counting on grounds that it wasn't given proper access to observe.
At the same time, hundreds of thousands of votes were still to be counted in Pennsylvania, and Trump's campaign said it was moving to intervene in the existing Supreme Court litigation over counting mail-in ballots there.
Wisconsin and Michigan are critical in the race to the 270 electoral votes in the state-by-state Electoral College needed to win the White House.
Trump, who made attacking the integrity of US elections a central campaign theme, in the early-morning hours falsely claimed victory in the election and made unsubstantiated allegations of electoral fraud.
"We were getting ready to win this election. Frankly, we did win this election," he said before launching an extraordinary attack on the electoral process.
"This is a major fraud on our nation. We want the law to be used in a proper manner. So we'll be going to the US Supreme Court. We want all voting to stop."
Trump's campaign last night said it had filed a lawsuit seeking to stop the count in Michigan, asserting it had not been allowed to observe the opening of ballots.
Mr Biden led by 38,000 votes.
"Michigan's elections have been conducted transparently, with access provided for both political parties and the public, and using a robust system of checks and balances to ensure that all ballots are counted fairly and accurately," Ryan Jarvi, press secretary to Democratic Michigan Attorney General Dana Nessel, said.
Wisconsin officials finished their tally after an all-night effort, showing Biden with a lead of just over 20,000 votes, or 0.6pc.
The Trump campaign immediately said it would request a recount, which is permitted under state law when the margin is below 1pc.
Closely contested states including Michigan, Pennsylvania, Arizona, Nevada, Georgia and North Carolina were still counting votes.
Mr Trump led in the two Southern states, Georgia and North Carolina, as well as in Pennsylvania.
Mr Trump campaign manager Bill Stepien called the president the winner in Pennsylvania even though state officials had not completed the count.
"If we count all legal ballots, we win," Mr Stepien said, setting the stage for the post-election litigation over ballot counting.
Mr Trump continued to make unsubstantiated attacks on the vote-counting process on Twitter yesterday, hours after he appeared at the White House and declared victory in an election that was far from decided.
Both Facebook and Twitter flagged multiple posts from the president for promoting misleading claims.