Key results in this weeks US elections hung in the balance Thursday, two days after polling, with accusations flying of voter fraud and corruption, as several races appeared headed for recounts.
"The people of Florida deserve fairness and transparency," Rick Scott told reporters.
"Every Floridian should be concerned there may be rampant fraud happening in Palm Beach and Broward Counties."
Scott, who is the state's sitting governor, said he was ordering an official investigation into his own race.
The dramatic announcement prompted a tweet from President Donald Trump alleging a "big corruption scandal" while fellow Republican Marco Rubio accused Democrats of a coordinated effort to "steal the election."
Florida was also the site of bitterly-fought legal battles in the 2000 presidential election.
Those were halted by the US Supreme Court, and George W. Bush defeated Al Gore by 537 votes in Florida, giving him the edge in the electoral college and handing him the White House.
Both Scott's race for the Senate -- against Democrat incumbent Bill Nelson -- and the state's governor election appeared headed for mandatory recounts.
Meanwhile, the Democratic candidate for governor in neighboring Georgia was threatening legal action to ensure all votes were counted in her contest.
Another Senate race in southwestern Arizona that was previously called in favor of a Republican candidate was tilting toward the Democrat on Thursday night, official results showed.
The developments looked set to raise partisan tensions to fresh highs 48 hours after polls closed in US midterm elections that saw Democrats seize control of the House of Representatives, while Republicans maintained their grip on the Senate.
'Ready for any outcome'
Scott's lawsuits alleged a lack of transparency over the counting process and asked that further details be made public, as his lead continued to shrink to around 15,000 votes.
President Donald Trump, under fire over his sacking of his attorney general, leapt on the news.
"Law Enforcement is looking into another big corruption scandal having to do with Election Fraud in #Broward and Palm Beach," he tweeted. "Florida voted for Rick Scott!"
Rancor was also spilling into governors' races, where Andrew Gillum in Florida and Stacey Abrams in Georgia were aiming to become the states' first African-American leaders, but the contests were tilting in favor of their Republican rivals.
Unofficial results show Gillum trailing Ron DeSantis, a Trump-endorsed Republican, by just 38,515 votes out of 8.1 million cast, or 0.47 percentage points.
Since Tuesday's election, "it has become clear there are many more uncounted ballots than was originally reported," Gillum spokeswoman Johanna Cervone said, amid reports that ballots had yet to be counted in Democrat-leaning Broward County.
Gillum is "ready for any outcome, including a state-mandated recount," she added.
State law says a recount is mandatory if the difference in a race is within 0.5 percent. If the margin is within 0.25 percent, as it stood Thursday in the Senate race, a hand recount -- slower and more thorough than by machine -- is ordered.
Unusual voting discrepancies were also being reported in Broward County.
The South Florida Sun Sentinel said it analyzed voting patterns and found that of Broward ballots already counted, 24,700 residents voted for a governor candidate but did not pick a candidate for Senate.
The unusual pattern appeared in no other Florida county, the newspaper reported.
Meanwhile, Abrams trailed Georgia secretary of state Brian Kemp by 1.3 percent in their governor's race, but her campaign complained that Kemp proclaimed victory prematurely.
"All the votes haven't been counted," Abrams lawyer John Chandler told reporters, adding there were outstanding absentee and provisional ballots.
"We will litigate until we have determined that every person's vote has been counted," Chandler said.
Kemp is currently on 50.3 percent of the vote. Under Georgia law if that share falls below 50 percent it would trigger a run-off vote in December, the New York Times reported.
Amid mounting concern over Kemp's oversight role in elections, Kemp resigned Thursday as secretary of state, but repeated his assertion that he defeated Abrams.
"The votes are not there for her," he said.
In the Arizona Senate race, meanwhile, Democrat Kyrsten Sinema -- currently a congresswoman -- had pulled ahead to 932,870 votes against 923,260 for her opponent, Martha McSally, a Republican congresswoman.
A recount appeared possible in the neck-and-neck race that still had outstanding provisional and absentee ballots.