Joe Biden faces an uphill battle against the US president, with Donald Trump locking in early gains to win the country's most prized battleground state of Florida.
The race in Florida was officially called by The Associated Press, along with its 29 Electoral College votes, after the Trump campaign claimed victory there. Reports showed him capturing swaths of the Latino vote that had previously been loyal to Democrats.
"President Trump wins Florida," the campaign tweeted over a picture of Mr Trump giving the thumb's up.
Mr Trump and his Democratic challenger, Mr Biden, were locked in tight races across the country late on Tuesday night (local time), as election officials processed a historically high number of mail-in ballots.
Supporters of US President Donald Trump rally in front of Cuban restaurant Versailles in Miami early on 4 November. Source: AFP
The president also claimed the battleground states of Ohio and Iowa, while Mr Biden won Minnesota and New Hampshire, according to the Associated Press.
Races were too early to call in some other critical states, including North Carolina, Georgia and Pennsylvania.
But the president has retained many of the states he won back in 2016, with all eyes resting on the three northern states where he last surprised the Democrats: Michigan, Wisconsin and Pennsylvania.
While Mr Trump held early leads in those three states, much of that was built on Election Day voting that skewed Republican. Counting of Democratic-heavy mail-in votes in those streets is expected to take hours - or even days.
A worker waits for the next absentee ballot to be sorted through at the Central Counting Board in Detroit on 4 November. Source: Getty Images North America
Victory in Florida was widely seen by voting experts as crucial for President Trump's chances for a second term, after he won the state by just over one per cent in 2016.
The state has 29 Electoral College votes, seen as vital for his re-election chances.
Mr Biden appeared to outperform Hillary Clinton in the state, outside the Miami-Dade County that swung it towards Mr Trump.
President Donald Trump arrives to speak at the Trump campaign headquarters on Election Day. Source: AAP
The county includes much of Florida’s Cuban-American community, which the president had pinpointed as a voter population that could help him carry the state again.
Part of Mr Trump’s strength in Florida also reportedly came from an improved performance with the state’s large Latino population, relative to the 2016 election.
Mr Biden was leading in counties where Hispanics make up more than 20 per cent of the population, but Mr Trump’s share of the vote in those counties was larger than four years ago.
More than four in 10 Hispanic voters in Florida said they cast a ballot for Mr Trump, according to an Edison Research exit poll.
Mr Biden still has multiple paths to the 270 electoral votes he needs without Florida - winning Michigan, Wisconsin and Pennsylvania would be enough to give Mr Biden a victory.
Democratic presidential nominee Joe Biden (R) and wife Jill Biden address supporters during election night at the Chase Center in Wilmington, Delaware. Source: AFP
Fox News has projected Mr Biden would win Arizona, another state that voted for Mr Trump in 2016, which would give his challenger more options.
"We are confident about Arizona - that is a turnaround," Mr Biden said, as he addressed supporters in Wilmington late on Tuesday night.
"We also just called it for Minnesota and we are still in the game for Georgia ... We are feeling good about Wisconsin and Michigan."
Mr Biden added the election "ain't over until very vote is counted, every ballot is counted".
“It’s not my place or Donald Trump’s place to declare who’s won this election ... That’s the decision of the American people," he said.
Mr Trump has also tweeted he will make a statement "tonight", claiming a "big WIN".
In a second tweet, the president claimed that his opponents were trying to "steal" the election, which Twitter has flagged as "disputed" and "misleading" election content.
Additional reporting by Reuters, AFP.
