Millions of Americans have lined up at polling stations across the United States to choose between Republican Donald Trump and Democrat Kamala Harris in a historic presidential race that remains too close to call.

Voting was under way on Tuesday with no major disruptions, as both candidates spent Election Day urging their supporters to cast their ballots, stressing that the stakes could not be higher.

“Today we vote for a brighter future,” Harris wrote in a post on X, linking to a national directory of polling sites.

Today, we vote for a brighter future.

Polling locations across the country are open. Find yours at https://t.co/VbrfuqVy9P. pic.twitter.com/7pJzch0XJR

— Kamala Harris (@KamalaHarris) November 5, 2024

Harris spent part of the day calling radio stations in an effort to encourage her supporters to vote. “We’ve got to get it done. Today is voting day, and people need to get out and be active,” CNN quoted Harris as telling one radio station in Georgia.

Trump, on his X account, told voters: “I need you to deliver your vote no matter how long it takes”, slamming his opponents as “radical communist Democrats”.

He addressed the media after casting his ballot in Palm Beach, Florida, saying he felt “very confident” about his election odds.

“It looks like Republicans have shown up in force,” Trump said. “We’ll see how it turns out.”

He added: “I hear we’re doing very well.”

A race churned by unprecedented events – two assassination attempts against Trump, President Joe Biden’s surprise withdrawal and Harris’s rapid rise – remained neck and neck, even after billions of dollars in spending and months of frenetic campaigning.

More than 80 million Americans had already taken advantage of early voting options before Tuesday, either via mail or in person, and lines at several polling stations on Tuesday were short and orderly.

Some glitches of vote-counting technology were reported in Cambria County, Pennsylvania, and a local court granted a request by election officials to extend voting hours by two hours on Tuesday night.

Several states have taken extra security measures to protect voting places.

In Georgia, election workers have been equipped with panic buttons to alert officials to possible security threats and violence.

In Maricopa County, Arizona, the heated scene of voter fraud allegations in the 2020 election, the voter tabulation centre now looks like a fortress behind fencing, concrete barriers and security cameras and with drones and police snipers.

But there were few incidents reported on Tuesday. Two polling locations in Fulton County, Georgia were briefly evacuated after false bomb threats.

The Federal Bureau of Investigation (FBI) said it was “aware of bomb threats to polling locations in several states”.

Many appear to originate from “Russian email domains”, it said in a post on X, adding that none of the threats have been determined to be credible.

Stephanie Jackson Ali, policy director at the New Georgia Project, told Al Jazeera that threats made against polling places in Georgia are not a danger.

“The [Georgia] secretary of state’s office believes that they are from a Russian influencing troll farm, basically, so not anything that’s credible or local”, she said.

These threats were against polling places in heavily Black-populated areas, she said, including Democratic-voting Fulton County, where Atlanta is located.

“This signifies that the power of the Black vote in Georgia is substantial, the power of the rising electorate is substantial.”

The “rising electorate” she said, includes Black voters, new voters, LGBTQ voters and Latino voters, who live in Atlanta in higher percentages than they do in the rest of the mostly conservative rural areas of the state.

‘The American dream’

In Dearborn, Michigan, Nakita Hogue, 50, was joined by her 18-year-old college student daughter, Niemah Hogue, to vote for Harris. Niemah said she takes birth control to help regulate her period, while her mother recalled needing surgery after she had a miscarriage in her 20s, and both feared efforts by Republican lawmakers to restrict women’s healthcare.

“For my daughter, who is going out into the world and making her own way, I want her to have that choice,” Nakita Hogue said. “She should be able to make her own decisions.”

At a library in Phoenix, Arizona, Felicia Navajo, 34, and her husband Jesse Miranda, 52, arrived with one of their three young children to vote for Trump.

Miranda, a union plumber, immigrated to the US from Mexico when he was four years old, and said he believed Trump would do a better job of fighting inflation and controlling immigration.

“I want to see good people come to this town, people that are willing to work, people who are willing to just live the American dream,” Miranda said.

Trump’s campaign has suggested he may declare victory on election night even while millions of ballots have yet to be counted, as he did four years ago.

The former president has repeatedly said any defeat could only stem from widespread fraud, echoing his false claims from 2020. The winner may not be known for days if the margins in battleground states are as slim as expected.

No matter who wins, history will be made.

Harris, 60, the first female vice president, would become the first woman, Black woman and South Asian American to win the presidency. Trump, 78, the only president to be impeached twice and the first former president to be criminally convicted, would also become the first president to win non-consecutive terms in more than a century.

Opinion polls show the candidates running neck and neck in each of the seven swing states likely to determine the winner: Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin.

Reuters/Ipsos polling shows Harris leading among women by 12 percentage points and Trump winning among men by seven percentage points.