Millions of Americans were voting on Tuesday amid a once-in-a-lifetime pandemic to decide whether to reelect Donald Trump, one of the most polarizing presidents in US history, or to send Democrat Joe Biden to the White House.
A record-breaking number of early votes -- more than 100 million -- have already been cast in an election that has the bitterly divided country on edge and is being closely watched around the world.
The 77-year-old Biden, who served for eight years as vice president to Barack Obama, leads Republican incumbent Trump in national polls and in many of the battleground states that will decide the race.
The first polls close in several eastern states at 7:00 pm (0000 GMT) but the winner may not be known on election night -- or possibly even for days -- because of the huge number of mail-in ballots that need to be counted.
The 74-year-old Trump, who has repeatedly sought to cast doubt on the legitimacy of mail-in ballots and the counting of votes beyond Election Day, said voters had a right to a timely result.
"The whole world is waiting," he said during a visit to Republican National Committee offices in Arlington, Virginia.
"You can't have these things delayed for many days," Trump said, adding ominously that "a lot of bad things" can happen.
"We should be entitled to know who won on November 3," he said.
Trump, his voice slightly hoarse after addressing five rallies on a hectic final day of campaigning on Monday, expressed confidence he would win four more years in the White House.
"I think we're going to have a great night but it's politics and it's elections and you never know," he said.
In an interview with "Fox and Friends," Trump dismissed reports he may declare victory prematurely. "Only when there is victory," he said. "There is no reason to play games."
Biden, who is making his third bid for the presidency, began Election Day with a visit to the church where his son, Beau Biden, and first wife and daughter are buried, and to his childhood home in Scranton, Pennsylvania.
"I want to restore basic decency and honor to the White House," a mask-wearing Biden told supporters through a bullhorn.
The former senator from Delaware rallied voters later in Philadelphia, Pennsylvania, saying they need to choose "hope over fear, truth over lies, science over fiction."
- 'Scary' -
According to the US Elections Project, 101.2 million early votes -- over 70 percent of the total ballots in 2016 -- have been cast in an election seen as a referendum on Trump's tumultuous first term.
More than 65 million are mail-in ballots and several key states -- including Michigan, Pennsylvania and Wisconsin -- do not begin counting those until Election Day itself, fueling fears a final result could take days.
Many early votes are believed to have been cast by Democrats, and Trump is hoping for massive Republican turnout on Tuesday.
"We're seeing lines of people and they're wearing a lot of red material," he said during his trip to Republican headquarters.
In Miami, Juan Carlos Bertran, a 60-year-old Cuban-American mechanic, said Trump "seems better to me for the country's economy."
"Now I have two jobs," he said. "Before I only had one."
Casting her vote in New York, Megan Byrnes-Borderan, 35, said Trump's threats to challenge the election results in the courts were "scary."
"I believe that Trump will go through all odds to try to win the election," she said.
Another New York voter, Justin Rodriguez, 32, said he was voting for Biden. "I really don't like the tension," he said. "I think Trump has brought a lot more tension than we usually have."
The deep divisions sparked by the bruising election campaign have raised fears of unrest and in Washington and other cities, store owners have been boarding up their shops.
Despite Covid-19 cases surging in more than half of the 50 US states, Trump, who suffered his own bout with the virus in early October, has sought to play down the health crisis and promised an economic comeback. "We're turning the corner," he said.
- Senate majority in play -
Trump also sought to focus attention on the financial dealings of Biden's son Hunter while his father was vice president but the issue failed to gain much traction beyond right-wing news outlets.
While no evidence has emerged of any wrongdoing by Biden, Trump is reportedly the target of investigations by prosecutors in New York.
He was impeached by the Democratic-majority House for abuse of power and obstruction of Congress in January for seeking to dig up political dirt on Biden from Ukraine but acquitted by the Republican-controlled Senate.
Biden focused his attacks on Trump's handling of the pandemic which has left more than 232,000 people dead in the United States.
"We're done with the chaos! We're done with the tweets, the anger, the hate, the failure, the irresponsibility," Biden said at an election eve rally in Cleveland, Ohio.
Trump has lost ground among suburban women and his "law and order" response to protests for racial justice turned off many Black voters, who traditionally vote Democratic anyway.
Trump's handling of Covid-19 has led to a loss of support among seniors, according to the polls, but his backing remains strong among rural voters and whites without a college degree.
Besides the White House, all 435 seats in the House of Representatives are at stake and Democrats are expected to possibly expand their majority in the chamber.
Roughly one-third of the Senate is up for grabs and Republicans risk losing their 53-47 majority.
Biden, like Hillary Clinton in 2016, is expected to win the popular vote but it is the 538-member Electoral College that ultimately determines the winner of the White House race.
A candidate needs 270 electoral votes to win and it may come down to voters in the tossup states of Arizona, Florida, Georgia, Michigan, North Carolina, Ohio and Pennsylvania.
Trump is to host an election night party at the White House while Biden watches the returns at his home in Delaware with his vice presidential candidate Kamala Harris, the California senator who is the first Black woman to appear on a major party ticket.