Elections in the US state of Georgia that will decide control of the Senate are too close to call amid a nail-biting ballot count.
Republicans Kelly Loeffler and David Perdue are neck and neck with Democrats Raphael Warnock and Jon Ossoff, reports BBC.
US President-elect Joe Biden's Democrats need to win both seats to gain full control of Congress.
The Republican party of outgoing President Donald Trump needs only to win one in order to retain the Senate.
Ms Loeffler is taking on Mr Warnock and Mr Perdue is battling Mr Ossoff. All four candidates were in a dead heat with 88% of ballots counted from Georgia's 159 counties.
Both Republicans have a wafer-thin lead, but thousands of votes remain to be counted in the Atlanta suburbs such as DeKalb County, which is expected to go heavily for the Democrats.
More than three million votes - about 40% of the state's registered voters - were cast before Tuesday. Early voting was a key benefit for Mr Biden in November's White House election.
Meanwhile, Mr Trump - whose unsubstantiated claims that he was the victim of electoral fraud have left Republican strategists worried about turnout in Tuesday's Senate runoffs - continued to cast aspersions on the integrity of the vote in Georgia.
On Saturday, Mr Trump pushed Georgia's top election official Brad Raffensperger, a fellow Republican, to "find" enough votes to overturn Mr Biden's presidential election win in the state.
What do the exit polls say?
So far, exit polls show Georgians in a clean split over which party they want to control Congress: 49% favoured Republicans, while 48% said the Democratic party.
The demographics roughly matched that of November's election. Black voters made up 29% of the vote, and these voters favoured the Democratic candidates nine-to-one. The Republicans, meanwhile, were winning a majority of white voters.
And these surveys showed that most voters were repeating the choices they made in November. Georgians who supported Mr Trump were casting ballots for Mr Perdue and Ms Loeffler, while Biden supporters were doing the same for Mr Warnock and Mr Ossoff.
Meanwhile, Mr Trump's unproven claims of voter fraud may have eroded voter confidence in the election system. According to exit polls from Edison Research, around 70% of voters were very or somewhat confident their votes would be counted accurately, a nearly 15% drop from the 3 November election.
Exit polls typically include interviews with voters after they have cast their ballot. These include people who voted early and on election day. Only a small number of voters are interviewed for exit polls so the results can differ from the official count.