The former vice president is leading in Wisconsin, Nevada and Arizona and closing in on Trump in Georgia and Pennsylvania
Democrat Joe Biden crept nearer to victory over Donald Trump on Thursday in an exceedingly close US election that hinged on razor-thin margins in a handful of states, while the Republican president escalated his legal efforts hoping to slow down his opponent.
Biden, the former US vice president, was continuing to cut into Trump's leads in Pennsylvania and Georgia while retaining slim margins in Nevada and Arizona.
Ballot counting dragged on in those battleground states two days after polls closed, with protesters from both sides staging street demonstrations in major cities over the vote counting.
Trump, who during the long and rancorous campaign attacked the integrity of the US voting system, again alleged voting fraud without providing evidence and accused Democrats of aiming to "steal" the election.
His campaign has filed several lawsuits and called for a recount in Wisconsin. His latest move was a lawsuit announced on Thursday alleging voting fraud in Nevada.
The vote counting was the latest tense chapter in a dramatic campaign focused on whether Americans should give Trump four more years in office after a tumultuous first term or turn to Biden, a figure on the national stage for a half century who promised to deliver steadiness rather than turmoil.
Trump tapped into discontent and pursued "America First" populism while Biden vowed to reverse many of Trump's actions at home and repair overseas alliances.
Some legal experts called Trump's challenges a long shot unlikely to affect the eventual outcome of the election, one of the most unusual presidential races in modern US history due to the coronavirus pandemic.
Concern about the virus caused a huge jump in people voting by mail, delaying the results.
Biden was leading in Wisconsin, Nevada and Arizona and closing in on Trump in Georgia and Pennsylvania.
"Be patient, folks," Biden wrote on Twitter. "Votes are being counted, and we feel good about where we are."
Multiple Trump lawsuits and a recount request would have to succeed and find in some cases tens of thousands of invalid ballots to reverse the result if Biden does prevail.
"What we are seeing on these legal suits are that they are meritless, and nothing more than an attempt to distract and delay what is now inevitable: Joe Biden will be the next president of the United States," Biden's campaign manager Jen O'Malley Dillon told reporters.
Trump's campaign predicted victory, with campaign manager Bill Stepien saying, "Donald Trump is alive and well" in the election.
Some of the outstanding votes in Georgia and Pennsylvania were clustered in places expected to lean Democratic — like the Atlanta and Philadelphia areas.
In Georgia, officials expressed hope that they would have a result by the end of Thursday. Trump's eroding lead stood at around 13,500, with about 2% of the ballots remaining to be tallied.
Trump's lead was about 114,000 votes in Pennsylvania, with about 8% of the ballots left to be counted.
Trump has to win the states where he is still ahead, including North Carolina, plus either Arizona or Nevada to triumph and avoid becoming the first incumbent US president to lose a re-election bid since fellow Republican George HW Bush in 1992.
Biden led in Nevada by about 11,400 votes and in Arizona by about 68,400 votes.
The president lashed out on Twitter and in a campaign statement in which he said: "If you count the legal votes, I easily win the election! If you count the illegal and late votes, they can steal the election from us!"
Trump wrote on Twitter, "STOP THE COUNT!" and "STOP THE FRAUD!" although he has no authority over ballot counting. He added that "all of the recent Biden claimed States will be legally challenged by us.
Despite Trump's allegations, US election experts have said fraud in balloting is very rare.
To capture the White House, a candidate must amass at least 270 votes in the state-by-state Electoral College. Such electoral votes are based largely on a state's population.
STOP THE COUNT!— Donald J. Trump (@realDonaldTrump) November 5, 2020
Edison Research gave Biden a 243 to 214 lead in Electoral College votes on Thursday after calling a district in Maine, which splits its state’s Electoral College votes, for Trump. All major news outlets said Biden had won Wisconsin, which would give him another 10 votes.
Trump, who has often relished legal battles during his long and turbulent business career, was at the White House working the phones and monitoring developments on television, two Trump advisers said.
He has been talking to state governors as well as close friends and advisers and dispatched some of this closest advisers out in the field to fight for him.
Biden has largely remained at home in Delaware and has consulted with aides including legal adviser Bob Bauer.
The exceedingly close election has underscored the political polarization in the United States and the deep divisions along racial, socioeconomic, religious and generational lines as well as between urban and rural areas.
After a summer of protests against racism and police brutality, some of which led to violence and looting, authorities are worried about mass demonstrations around the election but protests so far have been peaceful.
Demonstrators rallied in cities including Philadelphia, Washington, Phoenix and Detroit, for the second day in a row on Thursday.
Supporters of both candidates appeared outside a vote-counting centre in Philadelphia on Thursday.
A group of Trump backers held Trump-Pence flags and signs saying: "Vote stops on Election Day" and "Sorry, polls are closed." Across the street were Biden supporters, who danced to music behind a barricade.
Similar rallies were planned later in the day in Harrisburg, Pennsylvania's capital.
The counting and court challenges set the stage for uncertainty before December 8, the deadline to resolve election disputes. The president is sworn into office on January 20, 2021.
The Trump campaign said its Nevada lawsuit would allege a series of voting irregularities in populous Clark County, which includes Las Vegas, such as voting by people who left the state or were dead.
Former Nevada attorney general Adam Laxalt and other campaign figures who announced the lawsuit gave no evidence to support their allegations and refused to answer questions from reporters.
"My response is that we are not aware of any improper ballots that are being processed," Joe Gloria, the Clark County registrar, told reporters, adding that Trump's campaign has not presented him with any evidence showing otherwise.
In Pennsylvania, Trump's campaign and other Republicans have already filed various legal challenges. An appeals court in Pennsylvania on Thursday ordered that Trump campaign officials be allowed to more closely observe ballot processing in Philadelphia.
The campaign on Wednesday also filed lawsuits in Michigan and Georgia. Judges on Thursday dismissed both suits.
Biden had drawn about 3.6 million more votes than Trump nationwide. Trump defeated Democrat Clinton in 2016 after winning crucial battleground states and securing the Electoral College win even though she won about 3 million more votes nationwide.