President Donald Trump, meanwhile, has prepared his own pitch to keep the chamber in Republican hands.

The Georgia races respectively pit incumbent Republicans, Kelly Loeffler and David Perdue, against Democratic challengers Raphael Warnock and Jon Ossoff.

"It's a new year and tomorrow can be a new day for Atlanta, for Georgia and for America," Biden said at his event in the state's capital, while criticising the outgoing president.

He said the Trump administration had "gotten off to a god-awful start" with the slow rollout of COVID-19 vaccines.

"The president spends more time whining and complaining than doing something about the problem," he said.

He said the Democratic candidates, if elected, would ensure $US2000 ($A2600) stimulus cheques were delivered to Americans as the economy struggles.

Long solidly Republican, Georgia surprised the nation in November by backing a Democratic presidential candidate for the first time in almost three decades.

That has raised liberals' hopes for Warnock and Ossoff, although they face an uphill battle and need twin victories to deny Republicans a Senate majority they could use to block Biden's legislative agenda.

Later on Monday, Trump was due to address a rally in Dalton, a city in Georgia's heavily Republican northwest.

The duelling appearances illustrate the high stakes of the contest, in which 3 million have already voted.

A sweep by the two Democrats would hand control to Biden's party, as Vice President-elect Kamala Harris would hold the tiebreaking vote in the 50-50 chamber.

That would make it easier for Biden to enact further coronavirus relief and tackle climate change, as Democrats also control the House of Representatives.

None of the Senate candidates won a majority in the November 3 election, which spurred the run-off elections.

Trump continues to assert, without evidence, that his loss in November was the result of widespread voter fraud - a claim soundly rejected.

In a call on Saturday to Georgia Secretary of State Brad Raffensperger, Trump pressured the Republican official to "find" enough votes to overturn his defeat.

He suggested Raffensperger's failure to alter the November results could hurt Republican turnout in the Senate runoffs.

"There's nothing wrong with saying, you know, that you've recalculated," Trump said, according to an audio recording of the call released by the Washington Post. Raffensperger refused his request.

Democrats and election experts say Trump's efforts almost certainly broke the law.

Biden, who won Georgia by almost 12,000 votes, did not mention the call directly on Monday.

Loeffler said on Monday night she would object to the certification of the election results in Congress on Wednesday, joining about a dozen other Republican senators and over 100 Republican House members.

The move has virtually no chance of overturning Biden's victory.

It is not clear whether Trump's actions and his repeated claims of election fraud will affect the outcome of the Senate races.

Strategists say the outcome could likely hinge on how many Republican voters participate on Tuesday, given strong Democratic early turnout.

Australian Associated Press