Florida’s marquee governor’s race has heated up with the Trump-backed Republican candidate saying the state should not “monkey this up” by electing his opponent, Democrat Andrew Gillum, who is African-American, in November.

US Representative Ron DeSantis, a staunch supporter of President Donald Trump who won his party’s nomination on Tuesday, made the remarks on Fox News and immediately came under fire for their negative racial undertones.

“The last thing we need to do is to monkey this up by trying to embrace a socialist agenda with huge tax increases,” Mr DeSantis said, after calling Mr Gillum “an articulate” spokesman for far-left views.

Mr Gillum, the liberal mayor of state capital Tallahasee, won a surprising victory in the Democratic primary for Florida governor, and has said he hopes to motivate younger progressives and minority voters who normally sit out non-presidential elections.

If he wins the November 6 election, he would be the first black governor in the country’s most populous swing state.

“It’s disgusting that Ron DeSantis is launching his general election campaign with racist dog whistles,” Florida Democratic Party Chairwoman Terrie Rizzo wrote on Twitter.

It's disgusting that Ron DeSantis is launching his general election campaign with racist dog whistles. #FlaPol https://t.co/T9qRVYtbv3

— Terrie Rizzo (@TerrieRizzo) August 29, 2018

Words like “monkey” or “ape” have been used to demean African-Americans and are considered racist in that context.

Mr Gillum’s campaign referred Reuters to Ms Rizzo’s remarks, and several other members of Florida’s congressional delegation also condemned the comment.

Mr DeSantis spokesman Stephen Lawson said the candidate was referring to Mr Gillum’s political positions, not his race.

“Ron DeSantis was obviously talking about Florida not making the wrong decision to embrace” Mr Gillum’s policies, Mr Lawson said in a statement.

“To characterise it as anything else is absurd.”

However, Democratic Senator Bill Nelson, who is running for re-election against outgoing Republican Governor Rick Scott in November, wrote on Twitter that “Comments like Mr DeSantis’s are unacceptable in civilised discourse.”

Fox News host Sandra Smith, who interviewed Mr DeSantis, later said on air that the network does “not condone this language.”

Following Tuesday’s primary, the two parties are looking to their most fervent supporters – progressive Democrats and Republican – for victory in the November 6 election.

The race will be closely watched for clues about the mood of voters and messaging ahead of 2020, when Mr Trump could be seeking re-election against a liberal Democrat.

More than 3.5 million people voted out of 13 million registered voters in the state for a turnout rate of 27 per cent, the highest for a non-presidential Florida primary since 2002.

-AAP