Americans cast their votes yesterday in a high-stakes presidential election that could see Republican President Donald Trump secure another four years in office, or his Democratic challenger Joe Biden seize the White House.

Trailing Mr Biden in national opinion polls, Mr Trump is seeking to avoid becoming the first incumbent president to lose re-election since fellow Republican George H.W. Bush in 1992.

Speaking to Fox News yesterday, Mr Trump said he expected victory in all the key states that will decide the election.

Mr Biden posted a video message on his Twitter feed and urged his supporters: "Today, vote for a new day in America."

Ordinarily, major TV networks and news outlets have been able to call the race before an official announcement, based on exit polls the day after the election.

This time, however, uncertainty looms, as the results may take days or weeks after a record number of mail-in ballots due to the pandemic. Further delays may also occur if absentee voting rules are contested in court.

The chances of the results being disputed are lower if either candidate appears to be headed for a big victory, but if ballots counted later swing the contest in favour of the Democrats, Mr Trump may follow through on his threat of not accepting the results.

In a sign of how volatile the election could be, buildings in several cities were boarded up and the National Guard was on standby for the possibility of violent unrest.