Democrat Andrew Gillum, the African American mayor of Florida state capital Tallahassee, conceded Tuesday in his acrimonious battle for governor with Ron DeSantis, a member of the House of Representatives and ardent supporter of President Donald Trump.

"We could not be more thankful for the support that was shown by each and every one of you all the way along this path. We recognize that, you know, we didn't win it tonight," he told supporters.

"Earlier this evening I called Mr Ron DeSantis and congratulated him on what we expect will be him as the next governor of the great state of Florida. 

"But I want you to know, I want you to know, I want you to know that in spite of our congratulating him on his victory this evening, nothing that we believe in is compromised."

The race was among the most watched in the US midterms, with Trump throwing his weight behind DeSantis and Gillum endorsed by former Democratic president Barack Obama and former presidential candidate Bernie Sanders.

In the dying days of the campaign, Trump branded Gillum a "thief" and accused him of running a corrupt city, without presenting evidence for his attack.

The FBI has been conducting a probe of alleged public corruption in Tallahassee, and while Gillum has said he has been told he is not the target, Republicans used the investigation as a cudgel against him.

DeSantis himself has been widely criticized for urging Florida voters not to "monkey this up" by electing Gillum, a comment denounced as racist.