File photo. / Reuters

Washington, United States

White House rivals Kamala Harris and Donald Trump racked up early wins Tuesday as the first key polls closed in one of the tightest and most volatile presidential elections in US history.

Republican Trump won several strongholds, including Florida, while Democrat Harris took a number of eastern states -- but there were no major surprises in early results, which are being watched anxiously across the United States and around the world.

Vote counting also started in Pennsylvania, Georgia and North Carolina -- three of the crucial battlegrounds expected to tip the balance in the neck-and-neck overall race.

Millions of Americans lined up to vote in an race with momentous consequences, which will either make vice president Harris the first woman in the world's most powerful job or handing a historic comeback to former president Trump and his right-wing "America First" agenda.

A final result may be known in hours -- or could take days.

In a stark reminder of the tension -- and fears of outright violence -- around the election, officials said 32 bomb threats were called into polling locations around Georgia.

Voting was temporarily suspended at five locations in the majority Black, Democratic stronghold of Fulton County while police checked for explosives.

The FBI said the threats appeared to originate in Russia, which is accused by Washington of trying to meddle in the election.

'Big victory'

In a possible preview of other election challenges, Trump took to social media to say there is "talk about massive cheating" in Philadelphia, the Democratic stronghold of crucial state Pennsylvania.

City officials rejected the charge.

Trump added as the first results came in that "we're going to have a big victory tonight."

The billionaire has still refused to accept his 2020 election loss, after which his supporters attacked the US Capitol.

There were fears of fresh violence if Trump loses and numerous buildings in central Washington were boarded up on Tuesday.

All eyes were on the seven key battleground states that Harris and Trump frantically crisscrossed in recent days.

Early results in other states gave Harris 27 electoral votes and Trump 105 -- with 270 being the magic number to win the presidency.

Polls for weeks have shown a knife-edge race between Harris and Trump, who at 78 would be the oldest ever president at the time of inauguration, the first felon president, and only the second in history to serve non-consecutive terms.

Harris, 60, would also be only the second Black and first person of South Asian descent to be president.

She made a dramatic entrance into the race when Biden dropped out in July, while Trump -- twice impeached while president -- has since ridden out two assassination attempts and a criminal conviction.

Harris spent the day in Washington calling radio stations and taking a few calls personally at a phone bank for voters.

"We've got to get it done. Today is voting day, and people need to get out and be active," Harris told Atlanta station WVEE-FM.

Trump voted in Florida near his Mar-a-Lago residence, saying he felt "very confident" and that he wanted to be "very inclusive."

Tech tycoon Elon Musk, who has backed Trump, said he planned to spend election night with the former president.

'Super excited'

Casting a ballot in Arizona, Trump backer Camille Kroskey, 62, said she was voting in person due to concerns about voting fraud.

"I want to make sure I drop my ballot where it's going to actually land somewhere," she told AFP.

Harris will hold her watch party later at Howard University in Washington, a historically Black college that she attended as a student.

"I'm a black woman. I'm an American. I'm super excited about the possibility of her becoming president," a tearful Camille Franklin, who also went to the college, told AFP.

Trump has vowed an unprecedented deportation campaign of millions of undocumented immigrants, in a campaign full of dark rhetoric.

Harris has hammered home her opposition to Trump-backed abortion bans in multiple states -- a vote-winning position with crucial women voters.

The election is meanwhile being watched closely around the world including in the war zones of Ukraine and the Middle East, anxious to see how the next Oval Office occupant deals with the conflicts.