Donald Trump has declared victory over Kamala Harris in the US presidential election as he stands on the cusp of a historic political comeback.

The Republican told his ecstatic supporters at a campaign party in Florida that they would usher in “a new golden age for America”.

He needs just one more state to officially take him over the winning threshold of 270 electoral college votes, according to projections by the BBC's US partner CBS. He would be the first former president to return to the White House in more than 130 years.

In more good news for Trump, his party is projected to win majority control of the Senate.

He told supporters in West Palm Beach on Wednesday morning: "This will truly be the golden age of America - that's what we have to have.

"This is a magnificent victory for the American people that will allow us to make America great again.

Elon Musk, the world's richest man and Trump mega-donor, was with the Republican nominee as the results came in.

Trump could be on track for a clean sweep of the seven swing states needed to win the White House and he might even win the overall popular vote nationally - a feat he fell short of when first elected in 2016.

He is projected to win Pennsylvania, North Carolina and Georgia. CBS says Wisconsin is leaning towards the Republican and he is ahead in the other so-called Rust Belt state of Michigan. The results are not final.

He also has a solid lead in Nevada, while the race remains tight in the other sun belt battleground of Arizona.

As expected, Trump has swept conservative strongholds from Florida to Idaho, while Harris won liberal states from New York to California, CBS projects.

The Democrat had been expected to address a crowd on election night at Howard University in Washington DC, where she was an undergraduate, but it emerged after midnight that she would not appear. (BBC)