Florida's Midterm votes in key races are to be recounted.

As heavily Democratic counties in South Florida scrambled to meet a deadline to report election returns, Republican Rick Scott's lead over Democrat Bill Nelson in the US Senate race shrunk to just 12,562 votes out of nearly 8.2 million votes cast, ensuring a recount.

Vote totals posted today showed the margin in the marquee race in the nation's biggest battleground state at .015 per cent, close enough to trigger a recount by machine.

Also hitting that threshold was the race for governor between Democrat Andrew Gillum and Republican Ron DeSantis, who is sitting on a slightly bigger cushion of 33,684 votes over Gillum.

In Broward and Palm Beach counties, lawyers from both parties quibbled over ballots in which the intent or eligibility of the voter was in doubt as the minutes ticked toward a noon local time deadline.

Scott's narrowing lead as vote-counting continued has provoked litigation and raucous street protests reminiscent of the contentious 2000 election between George W. Bush and Al Gore, that forced the retirement of paper punch-card ballots famed for creating hanging chads.

The tight races underscored Florida's status as a perennial swing state where elections are often decided by the thinnest of margins. Since 2000, when Florida decided the presidency by 537 votes in a contest that took more than five weeks to sort out, the state has seen many close elections, but never so many dead heats in one year.

Scott, who has also raised allegations of fraud, used his bully pulpit to encourage Florida sheriffs to keep an eye out for any violations of election laws. President Donald Trump made accusations of "election theft".

But the claims by the President and the Governor were undercut by the Florida Department of State, which said in a statement that it found "no evidence of criminal activity at this time". The department, which oversees elections, had sent two monitors to observe Wednesday's vote in Broward County as result of a lawsuit over the mishandling of ballots in a 2016 congressional race.

A spokeswoman for the state department, Sarah Revell, said the observers were sent to "monitor the administration of the election, including visiting polling locations throughout the day as needed and observing preparation of the voting equipment and procedures for the election." The monitors have continued to monitor the vote-counting.

Nelson has accused Scott of using the power of his office to try to secure his Senate victory. Earlier, the governor called for state law enforcement to investigate the voting in South Florida - a probe that the state agency has so far declined to begin because the state department has not presented any allegations of fraud.

Under Florida law, a statewide machine recount is conducted when the margin of victory is less than 0.5 per cent, and a manual recount is ordered if the margin is less than 0.25 per cent. The governor's race does not appear to meet the manual recount standard.

A manual recount is defined as "a hand recount of overvotes and undervotes set aside from the machine recount," focusing on ballots in which voters skipped a race or voted for two candidates in one race.

Officials from both parties have focused much of their ire on Brenda Snipes, supervisor of elections in Broward County, Forida's second-largest county and the site of the "hanging chads" and other ballot irregularities during the 2000 presidential recount.

In a brief interview, Snipes brushed off the criticism. "It's kind of like a hurricane, where things get really stirred up for a while and then it passes," she said. "I don't know when this will pass, but it will."

The battle is also playing out on a national level, as the Scott campaign arranged for Senator Lindsey Graham, (R), to complain about the vote-counting in a call with reporters. He compared the situation in Florida to the contentious confirmation of Supreme Court Justice Brett Kavanaugh.

Graham encouraged Scott to report to Washington next week for orientation for new senators, regardless of the recount. "If the recount goes, the recount goes," said Graham.

Scott campaign manager Jackie Schutz Zeckman said the governor's team was still working on his schedule.

- Additional reporting AP, Bloomberg