WASHINGTON    -  Americans were voting on Tuesday under the shadow of a surging coronavirus pandemic to decide whether to reelect Republican Donald Trump, one of the most polarizing presidents in US history, or send Democrat Joe Biden to the White House.

A record-breaking number of early votes -- some 100 million -- have already been cast in an election that has the country on edge and is being closely watched in capitals around the world.

The 77-year-old Biden, who served for eight years as vice president to Barack Obama, leads Trump in national polls and in many of the battleground states that will decide the White House.

The former senator from Delaware, who is making his third bid for the presidency, began his day with a visit to the church in Wilmington, Delaware, where his son, Beau Biden, and first wife and daughter are buried.

Trump, 74, who is seeking to become the first US president to win reelection after being impeached, dismissed the polls showing him trailing Biden.

"I think we have a very solid chance of winning," he said Tuesday morning on "Fox and Friends." "We think we're doing very well everywhere. The crowds have been incredible." "Our country can never be the same country if they win," Trump said, adding that America would become a "socialist" nation. 

At the same time, Trump has cast doubt on the integrity of the election and threatened legal challenges, claiming the only way he can lose is if the results are "rigged."

Casting her vote in New York, Megan Byrnes-Borderan, 35, said Trump's threats were "part of why it is so scary." "I believe that Trump will go through all odds to try to win the election," she said.

Trump has waged a campaign against mail-in voting for months, claiming it could lead to fraud and all ballots should be tabulated on Election Day.

Several states, including battlegrounds Michigan, Pennsylvania and Wisconsin, do not begin counting mail-in ballots until Election Day itself.