Former US President Donald Trump Tuesday said he is "very confident" about winning back the White House after casting his vote in Florida in one of the most hard-fought elections.

Speaking to reporters outside a voting facility in West Palm Beach, Trump said he ran a "great campaign" against his rival Kamala Harris, a Democrat wild card entrant in the elections after Joe Biden decided to opt out after stumbling in his debate with Trump.

"If I lose an election, if it's a fair election, I would be the first one to acknowledge it. So far I think it's been fair," Trump was quoted as saying by AFP.

"They spend all this money on machines... If they would use paper ballots, voter ID, proof of citizenship, and one-day voting, it would all be over by 10 o'clock in the evening. It's crazy," he told reporters in West Palm Beach as quoted by AFP.

"Do you know that paper is more sophisticated now than computers? If it's watermarked paper you cannot... It's unbelievable what happens with it. There's nothing you can do to cheat," he added.

As the countdown to the most-anticipated US election ends, Americans queue up on Tuesday to decide who between Republican candidate Donald Trump and Democrat nominee Kamala Harris would occupy the White House next four years.

The build-up to the final stage of the election has been quite a dramatic one with two assassination attempts at former US President Donald Trump during his campaign phase and Kamala Harris entering the poll race in a surprising move.

If voted to power, Kamala Harris will create history by becoming the first woman, Black, and Asian-American to lead the nation.

Meanwhile, Arizona is one of the seven swing states that has emerged to become a pivotal player in this election with wide gender divides on issues including reproductive rights, immigration, and the economy.

Besides, the other neck-to-neck battlegrounds are Georgia, Michigan, Nevada, North Carolina, Pennsylvania, and Wisconsin, as per opinion polls.

Voting across the country began at 6 am local time on the final election day. Since the US is divided into different time zones, the eastern part of the country was the first to vote.

Although voting ends Tuesday, the winner may not be known for days if the margins in the key states continue to remain slim as predicted.