Donald Trump has hailed a “big win” and accused his opponents of “trying to steal the election”, while Joe Biden has stressed the tight race is not over and that his campaign for the presidency is still “on track” for victory.

In a nail-biting contest that is still too close to call, the Republican incumbent made big gains with results better than polling had anticipated and wins in the fiercely-contested bellwether states of Florida and Ohio.

But most swing states are yet to be announced and his Democratic challenger still had a route to win the White House, with early votes putting him ahead in Arizona, where a victory would be a major coup in the former Republican stronghold.

Despite the uphill battle, Mr Biden took to a stage in Delaware to say “we’re feeling good about where we are”, while hoping for gains in swing states yet to be called, including Wisconsin, Michigan and Pennsylvania.

“I’m here to tell you tonight, we believe we’re on track to win this election,” he told supporters.

“We knew because of the unprecedented early vote, the mail-in vote, that it’s going to take a while, we’re going to have to be patient.

“It ain’t over until every vote is counted, every ballot is counted.”

But moments later Mr Trump tweeted to repeat his unsubstantiated claim that his opponents are trying to “steal” the election after a divisive race that has been overshadowed by the coronavirus pandemic.

“A big WIN!” Mr Trump wrote, promising a further statement.

“We are up BIG, but they are trying to STEAL the Election. We will never let them do it. Votes cannot be cast after the Polls are closed!”

Twitter quickly placed a warning on the tweet to say his claim is “disputed”, with the social media giant telling users he was making a “potentially misleading claim” about the election.

Mr Biden’s campaign had prepared for Mr Trump to make an early call of the election, and for him to falsely claim that votes being counted after election night are fraudulent.

Florida, and its 29 electoral college votes, was a must-win for Mr Trump to reach the 270 required for victory, with no Republican having won the White House without the Sunshine State’s support since 1924.

It has backed the winner in every election since 1996 and has only gone with the losing candidate twice since 1928.

Ohio is also a major victory for Mr Trump, having been key to his chances of remaining in the White House, and whoever has won the state has gone on to take the presidency since 1964.

But the two contenders were still in a knife-edge race, with Mr Trump holding onto Texas and claiming the battlegrounds of Ohio and Iowa, while Mr Biden won modest victories in Minnesota and New Hampshire.

Mr Biden said he is “confident” about winning Arizona, “feeling real good” about Wisconsin and Michigan and is “still in the game” in Georgia.

It could take days for the victor to emerge, with officials saying counting could continue throughout the week in the key states of Michigan and Pennsylvania.

The lack of clear winner and claim and counterclaim raised fears of unrest on the streets of America after one of the most divisive campaigns in history.

Mr Biden, a former vice president, has painted the election as the “battle for the soul” of the nation, saying democracy itself is at stake. Mr Trump has reprised his “Make America Great Again” mantra.

Economic fairness and racial justice have been key issues in the election race. Both men have also clashed over the Covid-19 response as the nation reels from more than 230,000 coronavirus deaths and millions of job losses.

Mr Trump has sought to downplay the pandemic’s effect, saying the nation is “rounding the corner”. But his opponent has accused the president of having surrendered to the disease.

Steady lines of voters flocked to the polls on Tuesday after around 100 million Americans voted early, setting the nation on course for a record turnout figure.

National polls have consistently put Mr Biden ahead, but the race was predicted to be closer in the battleground states.

Each state gets a number of electoral college votes roughly in line with its population and they largely hand them all to the winner in that state. With 538 up for grabs across the States, 270 is the key number to win the presidency.

But the election night itself looked unlikely to reveal the definite answer many want with results as close as they were.

Mr Trump had already jeopardised the likelihood of a simple race by refusing to commit to a peaceful transition of power and having warned of a “rigged election”.

Along with his attacks, which have largely centred on unfounded claims over postal voting, he has threatened to challenge the result in the courts if it is not in his favour.

The president has invited hundreds of supporters to an election party inside the White House. Mr Biden will await the results in his hometown of Wilmington, Delaware.