The first states have been called by Associated Press in the US election, with Republican nominee Donald Trump and his Democratic rival Kamala Harris dominating in their traditional heartlands.
Polling booths remain open in parts of the country, and counting will continue through the night — and subsequent days.
None of the states that had been declared were a surprise, with Trump claiming jurisdictions like West Virginia and Kentucky, and Harris winning Vermont.
There were promising early signs for both candidates in the key battlegrounds of Georgia, Pennsylvania and North Carolina.
Trump had an early lead in Georgia as he looks to flip the state, but Harris was ahead in North Carolina and Pennsylvania, although there was a lot of counting to come in all three.
Many analysts predict the election will go down to the wire, and be among the closest in the country's history.
However, in the final week of the campaign, multiple polls predicted Harris, the US vice-president, was enjoying a late surge of support among voters in multiple critical swing states.
[Overall No Map]Earlier on Tuesday, local time, Harris used a radio interview broadcast in the battleground state of Georgia to encourage people to vote, saying her and Trump had "different visions of the future of our nation".
Trump, meanwhile, cast his vote at Florida's Mandel Recreation Centre on Tuesday, and told reporters he felt "very confident" of victory.
"It looks like Republicans have shown up in force," he said.
Polls start to close
In the US, each state runs voting in its own way. In some states, paper ballots are used while others have electronic voting machines.
Polls close at different times depending on where you are in the country, and votes are counted in distinct ways.
It means that if the result is close, a final tally may not be known for several days.
Most eyes are on seven critical swing states: Arizona, Georgia, Wisconsin, Michigan, Nevada, North Carolina and Pennsylvania.
The latter is rated particularly important to victory, because it holds 19 electoral college votes.
Under the US presidential election system, different states carry different numbers of electoral college votes, and the successful presidential candidate must reach at least 270.
While the first polling places closed at 6pm on Tuesday (10am Wednesday AEDT), the last ones will not shut until midnight (4pm AEDT).
After a frenetic week of campaigning across swing states, often hitting several on one day, both candidates decamped for a quieter day as the country votes.
Harris is watching the count from Washington DC, at an election night party at Howard University, a historically Black university where she graduated in 1986.
After returning form Michigan in the early morning, former president Trump is holding a watch party at Mar-a-lago in Palm Beach, Florida.
Voting calm despite alert
Authorities are on high alert in multiple parts of the country, as results come in.
In the capital city, Washington DC, temporary fences have provided extra security around key government buildings, including the White House.
The insurrection on January 6, 2021 — the escalation of Trump's refusal to accept his 2020 presidential election loss — is still very much in the city's consciousness.
Elsewhere, people have been warned not to intimidate or attack workers or voters at polling places.
On Monday evening, Larry Krasner, the Pennsylvania district attorney, warned people not to "f*** around" with the election.
"We do have the cuffs, we do have the jail cells," he said.
Despite the preparations, voting took place amid relative calm around the country.
In Georgia, polling was interrupted at several polling places after bomb threats. A judge later ruled the affected locations could stay open later.
