Americans were voting in large numbers on Tuesday in one of the most divisive bitter presidential elections in decades in which incumbent Republican Donald Trump is challenged by Democrat Joe Biden.

Amidst a resurgent COVID-19 pandemic, nearly 100 million people have already cast their ballots in early voting, putting the country on course for its highest turnout in a century. Some 239 million people are eligible to vote this year.

The mail-in ballots could take days or weeks to be counted in some states - meaning a winner might not be declared in the hours after polls close on Tuesday.

There is an estimated four million Indian-American population of which about 2.5 million are potential voters in the November 2020 presidential elections. Over 1.3 million Indian-Americans are voters in key battleground states, including Texas, Michigan, Florida and Pennsylvania.

Large lines were seen and hundreds of people had queued up before polling stations, in particularly in the key battleground States like Pennsylvania and Wisconsin.

The timing of the start of the polling differs from State to State, mainly due to the different time zones. People mostly in the East coast started trickling down to the polling stations as many States opened up the polling stations at around 6 am (4.30 pm IST). These States include Virginia, New York, New Jersey, and Maine. Polling in California starts at 7 am (8.30 pm IST).

Initial reports indicated an early large turnout. In the battle ground State of Pennsylvania, hundreds of people were seen outside polling booths even before the start of the polling.

Trump who returned from campaigning in the wee hours of Tuesday urged Americans to vote for him. “VOTE, VOTE, VOTE!” Trump said in a tweet with a short video of him dancing at election rallies.

"Vote like your freedoms, your livelihood, and our future depends on it… Because they do!” said Trump, who is seeking to avoid becoming the first incumbent president to lose a re-election since George HW Bush in 1992.

Biden also tweeted urging people to vote. "It's Election Day. Go vote, America!” he tweeted.

"In 2008 and 2012, you placed your trust in me to help lead this country alongside Barack Obama. Today, I'm asking for your trust once again — this time, in Kamala and me. We can heal the soul of this nation — I promise we won't let you down," Biden tweeted.

Biden's running mate, Kamala Harris, urged voters to not to "allow anything to come between you and your vote. If you have any questions or concerns about voting, reach out to our voter hotline."

In another tweet, she said, "If you've already voted, thank you. But we still need your help. Take 20 minutes to help voters in critical battleground states find their polling location. This election is too important to leave anything to chance."

Poll experts said that the turnout is going to be the key in the election results.

Trump is expected to visit a Republican election office in Arlington, a Virginia suburb of Washington DC. Biden started his day with a visit to Church for prayer and participate in a mass. Thereafter, he was scheduled to travel to the battleground State of Pennsylvania for campaign stops.

In the evening, Biden and Harris will address the nation on Election Night in Wilmington, Delaware. Trump is scheduled to watch the election results from the White House. He has invited a select guests at the White House.

National polls continue to show Biden leading Trump, by a comfortable 8 percentage points.

US elections, however, are not determined by the national popular vote, but rather in the 538-member Electoral College, with each candidate needing a majority of 270 to win the presidency.

In all but two of the country's 50 states, either Trump or Biden will win all the electors from each state by winning the popular vote there, with the most populous states holding the most electors.

The coronavirus pandemic is a major topic during this election. The US has recorded more cases and more deaths than any other country worldwide, reporting more than 81,000 new infections on Sunday alone. Some 9.2 million people are also affected by the disease.

The US economy saw record-breaking 33 per cent growth in the third financial quarter of this year, following a record 31 per cent contraction in the second.

The November 3 presidential election has been billed as one of the most divisive in recent American history.

Before the campaign closed, 74-year-old Trump toured the key voting battlegrounds of Wisconsin, Michigan, North Carolina and Pennsylvania while his 77-year-old rival campaigned in Pennsylvania and Ohio, urging Americans to back them in the race for the White House.

"To all of our supporters: thank you from the bottom of my heart. You have been there from the beginning, and I will never let you down. Your hopes are my hopes, your dreams are my dreams, and your future is what I am fighting for every single day!" Trump tweeted past midnight.

"A vote for Sleepy Joe Biden is a vote to give control of government over to Globalists, Communists, Socialists, and Wealthy Liberal Hypocrites who want to silence, censor, cancel, and punish you. Get out and VOTE #MAGA tomorrow!," the president wrote in another tweet, attacking Biden.

The Republican Party in a tweet said, “Let's Make America Great Again and re-elect our fantastic president!”

Biden, the former US vice president, said he was "running as a proud Democrat, but I will govern as an American president."