Washington D.C. - Election day in the United States is officially underway, with the main spotlight focused on the race for the White House between President Donald Trump, who is seeking a second term, and his rival, the veteran Democrat Joe Biden.

Two small towns in the north-eastern state of New Hampshire kicked off the vote with their traditional midnight opening of polling stations.

Some major cities on the east coast will see polling stations open at 6 AM. Afterwards, polls will open across six time zones over the 50 states taking part in the election. The final polls will close in Alaska, in the far west, when it's already morning in the east.

Across the country, some 100 million people have already voted, through mail-in ballots, early in-person voting, drive-thru polls and other means. The number has skyrocketed this year, as various localities expanded early voting because of the coronavirus pandemic.

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In 2016, nearly 140 million people voted in total and observers are speculating that this year turnout could break records.

With Biden consistently leading in the polls including in crucial swing states, Trump, a Republican, is fighting to hold on to the White House after a turbulent four years in office. The outcome, however, is far from certain.

Voters across all states are also casting ballots on a range of other issues, including for 35 Senate seats, the entire House of Representatives, numerous state and local offices and a slew of referendums on issues from tax policy to drug laws.

The campaigns are expected to stay on the road until the last minute, trying to garner every vote they can in places like Pennsylvania and Florida, states that seem to be split down the middle and carry significant weight in the Electoral College.

In the race for president, the national popular vote is not what counts. Rather each state is awarded a number of Electoral College votes based on its population size – the winner must seize a majority. Several key states are expected to determine the outcome.

Trump spent the last day before the election not only bashing his opponent, but also attacking the Supreme Court and alleging without proof that there will be serious fraud in the election, as he showed no sign of toning down his rhetoric in the final stretch.

His rhetoric on fraud has alarmed some Democrats. Both campaigns are poised to battle in the courts.

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Biden is pledging to end the "chaos" of the Trump era and get a better grip over the pandemic, accusing the incumbent of having bungled the response. More than 230,000 people have died in the US from Covid-19.

The Biden camp has said they will not let Trump unilaterally declare himself the victor on election night. Because of the mail-in voting, a result may not be clear for days or longer.

For many voters, the key issues in the election are the pandemic, the economy and health care, along with more specific areas such as gun rights and control, the environment, and abortion.

Trump is running as a conservative, while Biden has embraced some progressive ideas but has mainly pitched a wide tent, trying to build a broad coalition.