Jubilant Biden supporters have partied into the night to celebrate the Democrat becoming president-elect, letting loose after several days when the result appeared on a knife-edge.
People honked their horns and hung out of car windows in cities such as Chicago and Washington, others danced and hugged, while some banged pots and pans, and others paraded with cut-outs of the new president.
There were tears among some in New York's famous Times Square as they looked up at screens showing Mr Biden and Kamala Harris making their victory speeches on Saturday night.
More than 1,000 supporters at a drive-in rally in Delaware cheered America's incoming leader as he made a passionate speech pledging to unify the country.
The party was triggered after Mr Biden took the key state of Pennsylvania to seal his presidential win - despite Donald Trump's insistence he will fight the result amid unfounded allegations of fraud.
Some of the biggest celebrations were not far from the White House itself, with Biden supporters gathering on Black Lives Matter Plaza as fireworks rocketed into the sky.
In the city's Dupont Circle, several hundred people marched towards the centre to the sound of honking horns and clanging cowbells.
Duane Fitzhugh, 52, a teacher celebrated outside the Trump Hotel in Washington, and said it was as if a spell had been lifted.
"It's like a pall fell over the country four years ago, and we've been waiting years for it to end," he said.
Donna Thomas, another Washington resident said: "I jumped off the bus to come right down here to the White House. It is something to celebrate. We have been waiting so long."
Celebrations and spontaneous block parties also sprang up in New York City.
People in Washington Square Park in Greenwich Village danced and jumped in the park's fountain, a planned demo in Columbus Circle turned into a party, and people banged on kitchenware and honked their horns in many neighbourhoods.
In San Francisco's famous Castro district, a pinata effigy of President Trump was paraded around - with signs among the crowd reading "you're fired" and "lock him up".
Kamala Harris - the vice-president elect - was also celebrated in Oakland, where block parties also broke out.
America's first woman and African-American vice president was born in the California city.
In Boston, police shut traffic from streets near the State House to allow people to party.
Supporters of President Trump also turned out in places - but their gatherings in states such as Pennsylvania, Michigan and Arizona - were smaller and more muted.
Hundreds gathered in Lansing, Michigan, waving Trump-Pence flags and shouting "this is not over" and "we will be here forever."
There were some isolated cases of rival groups confronting each other, such as in Harrisburg, Pennsylvania, where about 100 from each side faced off.
However, there were no immediate reports of violence.
In Phoenix, Arizona, some Trump supporters were carrying firearms as they chanted slogans like "Trump won" and "We will win in court."
Mr Trump's claims of voter fraud appear unfounded however, and he has yet to offer any evidence despite invoking the threat of taking his case to the Supreme Court.
