WILMINGTON (DELAWARE) - Democratic candidate Joe Biden was projected to win the crucial battleground states of Wisconsin and Michigan, strengthening his lead over United States President Donald Trump although the race remained too close to call past midnight in Singapore.
Mr Trump sought a recount in Wisconsin and mounted legal challenges to stop ballots being counted in Michigan, Georgia and Pennsylvania - all the key states he needs for a viable path to victory.
Michigan's 16 electoral votes and Wisconsin's 10 potentially give Mr Biden a total of 264 electoral votes - six shy of the 270 he needs to win the presidency. Mr Trump has 214.
Mr Biden will be able to claim the presidency if he wins any one swing state where counting is still ongoing: Nevada, where he holds a slim lead, and Georgia and Pennsylvania, where Mr Trump is ahead but with a margin that is narrowing.
Later-counted votes from absentee ballots, as well as from large urban areas that are Democratic strongholds, have the potential to drag Mr Biden over the line in Georgia and Pennsylvania.
He will also need to hold Arizona, a close race that Fox News and the Associated Press have already called for him. His lead over Mr Trump narrowed slightly as the state's largest county, Maricopa County, released more results.
Pro-Biden protesters in cities across the US demanded that every vote be counted, while pro-Trump crowds gathered outside counting centres in Arizona and Michigan demanding a stop to vote-counting.
Mr Biden said it was clear he would have enough electoral votes to win the presidency, calling for unity after an election season marked by rancour and division.
"I am not here to declare that I have won. I am here to report that when the count is finished, I believe I will be the winner," he said in a speech from his home town of Wilmington, Delaware.
On Thursday morning, his campaign manager Jen O'Malley Dillon and senior adviser Bob Bauer said that victory was imminent and expected on Thursday.
Ms O'Malley Dillon said Mr Biden was "nearing parity" with Mr Trump in Pennsylvania and projected that most of the remaining ballots there would give the Democrat the win. She also said he was expected to win Nevada.
The Trump campaign's lawsuits were "meritless and nothing more than an attempt to distract and delay what is now inevitable", she said.
Mr Trump, who has been seeking for months to invalidate mail-in ballots and making unsubstantiated claims that they were susceptible to fraud, took to Twitter to complain about being overtaken in Michigan and elsewhere.
He alleged voter fraud, without evidence, and claimed victory in Pennsylvania, Georgia and North Carolina, even though all three states are still counting votes.
"ANY VOTE THAT CAME IN AFTER ELECTION DAY WILL NOT BE COUNTED!" Mr Trump said in a Tweet on Thursday morning, which Twitter flagged as misleading.
His campaign sought a recount in Wisconsin, where Mr Trump lost by 0.7 percentage point. Wisconsin law allows a recount if the margin between the top two candidates is less than 1 per cent.
Mr Bill Stepien, manager of the Trump campaign, said it was not given "meaningful access" to several counting locations in Michigan and has filed a suit to halt counting until access was given.
The Trump campaign also filed to join a lawsuit by the state's Republican Party challenging a Supreme Court decision to accept mail-in ballots received up to three days after election day. The ballots must be postmarked by election day.
With ballots still being counted, Mr Biden has already got about 72.1 million votes, taking 50.4 per cent of vote share according to AP and beating the previous record of 69.5 million votes set in 2008 by former president Barack Obama.
So far, Mr Trump has received about 68.7 million votes. He lost the popular vote by nearly three million votes in 2016, but beat Mrs Hillary Clinton on electoral votes.