Donald Trump and Joe Biden are each confident of victory in the US presidential election, as the outcome hangs in the balance with both sides embroiled in a legal fight over votes.
Vote counting is still going on in crucial battleground states that will decide the election.
Projected wins in the Rust Belt states of Michigan and Wisconsin have inched Mr Biden closer to victory.
As results trickle in, Mr Trump has challenged vote counts in key states.
The president has made unfounded assertions of victory and allegations of voter fraud, accusing Democrats of trying to "steal" the election.
Mr Biden stopped short of declaring victory, but said he was confident he was on course to beat his Republican rival.
The Democratic candidate is currently leading in Nevada and Arizona, while the gap is closing between him and Mr Trump as counting continues in Georgia and Pennsylvania.
Overall turnout in Tuesday's election is projected to be the highest in 120 years at 66.9%, according to the US Election Project.
Mr Biden had the support of 70.5 million voters, the most won by any presidential candidate ever. Mr Trump has pulled in 67.2 million votes, four million more than he gained in 2016.
The bitter election race was dominated by the coronavirus pandemic, which hit a new record high of 103,000 daily cases in the US on Wednesday, according to the Covid Tracking Project.
But the economy, which has been badly affected by the pandemic, was the most important single issue to voters, exit poll data indicated.
What are the campaigns saying?
As a tense wait for results continued on Thursday, both campaigns said their candidates were on track to win the White House.
Mr Biden's campaign manager Jen O'Malley Dillon said the initial results looked "very positive" for the former vice-president, but called for patience as counting votes was "going to take time".
"Our data shows Biden will be the next president of the United States," Ms O'Malley Dillon said. "That counting will continue to show our path to victory."
Mr Trump's campaign manager Bill Stepien appeared equally confident of the president's chances of winning in Pennsylvania and other states. This outlook, he said, was based on "numbers and data not gut or spin".
"Donald Trump is alive and well," Mr Stepien said.
However, as Mr Biden has gained ground, the Trump campaign has turned to the courts, filing lawsuits and demanding a recount in Wisconsin.
Mr Trump has attempted, without evidence, to sow doubt about the validity of ballots counted after election day and cast by mail. Counting ballots after election day is a legal, normal practice in a number of states.
Can Trump still win?
Mr Biden has 253 Electoral College votes, giving him the edge in the race to accumulate the 270 needed to win the White House. Mr Trump has 214.
In the US election, voters decide state-level contests rather than a single, national one. Each US state gets a certain number of electoral college votes partly based on its population, with a total of 538 up for grabs.
Now Mr Trump is projected to lose Wisconsin (10 electoral college votes), he must win Georgia (16 votes), North Carolina (15), Pennsylvania (20) and either Arizona (11) or Nevada (6) to prevail.
On Thursday afternoon, an election official in Georgia said there were about 48,000 votes left to count in the state. "We anticipate getting through this process today," a spokesman for Georgia's Secretary of State said, without giving a specific timeline. "Every ballot will be counted."
The gap between Mr Trump and Mr Biden has dwindled to about 13,000 votes in the state, the latest estimates suggest.
In Arizona, Mr Biden was leading by about 68,000 votes, with further results expected on Thursday. CBS has categorised it as a "likely" win for the Democrat. Supporters of Mr Trump gathered outside a vote counting centre in Maricopa County (which includes Phoenix, the largest city in the state), where officials vowed to "continue our job".
With tens of thousands of ballots yet to be counted in Nevada, Mr Biden has an edge over Mr Trump. An election official said the results from more than 51,000 mail-in ballots would be updated on Friday.
An even greater number of votes, an estimated 550,000, are yet to be counted in Pennsylvania. The "overwhelming majority" of those votes were due to be counted on Thursday, an election official told CNN.
What about the legal challenges?
The Trump campaign has launched a number of lawsuits demanding a halt to counts. But in states like Arizona and Nevada, where Mr Trump is currently marginally behind, his supporters are demanding that counting continues.
The campaign filed a lawsuit in Michigan to stop counting there because it contended it had been denied "meaningful access" to observe the opening of ballots and the tally. A state court judge dismissed the lawsuit on Thursday.
In Detroit, Michigan, police were called on Wednesday afternoon to guard the doors to a vote-counting facility as some protesters outside demanded access to monitor the process. According to the Detroit Free Press, there were already some 200 people observing the vote inside the building.
The Trump campaign also filed a lawsuit in Pennsylvania to press for closer scrutiny of the ballot counting process. The lawsuit was rejected by Pennsylvania's Supreme Court on Thursday, Fox News reported.
The president has a three-point lead in the Keystone State, but many thousands of votes remain to be counted.
Mr Trump has also started legal action against Georgia to halt the vote count there. His campaign said a Republican poll observer in the southern state had witnessed 53 late absentee ballots being illegally added to a pile of votes in Chatham County. Again, a state court dismissed the lawsuit on Thursday.
The latest legal bid was launched in Nevada on Thursday. The Trump campaign has alleged that around 10,000 votes were cast by people who no longer live in the state.
And in Wisconsin, Mr Trump's campaign said the president would formally request a recount, citing "irregularities in several Wisconsin counties".
Incomplete results indicate the margin between Mr Trump and Mr Biden in Wisconsin is less than one percentage point, which allows a candidate to seek a recount.
As things stand, Mr Biden is ahead by more than 20,000 votes. Election experts say recounts typically change tallies by only a few hundred.
In 2016, Mr Trump's wins in Wisconsin, Michigan and Pennsylvania sealed his victory and took him to the White House.
In the early hours of Wednesday, the president claimed he had won the election despite many uncounted votes remaining. The speech brought strong criticism from both Democrats and Republicans.
Mr Trump also said he was prepared to take the election to the Supreme Court, and his campaign is asking Republican donors to help fund legal challenges. Such challenges start at a state level but could eventually lead to the top court in the US.
Republican National Committee Chairwoman Ronna McDaniel said: "The fight's not over. We're in it."
Mr Biden's running mate, Kamala Harris, tweeted asking supporters to contribute $5 to help pay for litigation that could "stretch on for weeks".
Bob Bauer, a Biden campaign lawyer, said that the lawsuits the Trump campaign has filed against the counting of votes "don't have merit".
"It is to create an opportunity for them to message falsely about what's taking place in the electoral process," Mr Bauer said.