Hillary Clinton and Donald Trump embarked Saturday on a campaign blitz in the battleground state of Florida, a must-win if the Republican is to stop her becoming the first woman to win the White House.

There are just three days to go in America's ugliest, most divisive presidential election campaign in living memory. Tightening polls have seen both candidates pull out all the stops in a desperate attempt to win.

The 69-year-old former secretary of state, looking to make history as the first US female commander-in-chief, is commanding A-list superpower in that quest, pulling in Beyonce and Jay-Z at a concert in Cleveland on Friday.

Performances from Jon Bon Jovi, Katy Perry and Stevie Wonder are scheduled Saturday.

In contrast, the maverick billionaire who has inflamed the political establishment with his insult-dishing campaign is isolated, leaning on his family and only a handful of Republican politicians as surrogates.

While polls tightened in the last week, coinciding with the FBI's announcement that it has renewed scrutiny of Clinton's emails while secretary of state, forecasts still give the 69-year-old Democrat the edge.

Trump kicked off the weekend at a rally in Tampa on the Gulf Coast, while his Democratic opponent visited an early voting center in Miami ahead of a rally in Pembroke Pines in heavily populated southeastern Florida.

The real estate mogul mocked the free Jay-Z and Beyonce concert in Ohio that Clinton attended the night before, slamming the rapper's language.

"I like them both but he used language last night that was so bad and then Hillary said 'I did not like Donald Trump's lewd language,'" he said to laughter from supporters.

"I'll tell you what, I never said what he said in my life! But that shows you the phoniness of politicians and the phoniness of the whole system, folks."

Saturday's RealClearPolitics poll average gives Clinton a 2.3 percent lead on 45 percent to 42.7 percent for Trump in a four-way race. The same poll average gives her just a 1.2 percent lead over Trump in Florida.

In the last stretch, the former first lady is looking to hold onto her slender lead, while the New York real estate tycoon is desperate to close the gap in key swing states that could decide who secures an electoral college win.

Over the next 72 hours, the Republican is expected to canvas in Florida, North Carolina, Nevada, Colorado, Iowa, Pennsylvania and New Hampshire.

He said Saturday he was also going to Minnesota, a primarily blue state. Clinton has scheduled stops in Pennsylvania, Ohio and New Hampshire after her Florida swing.

The two candidates offer starkly different visions of America -- Clinton celebrating hope and Trump bashing a corrupt and venal establishment.

After a largely disciplined and on message week, Trump appeared to stray on several occasions in Tampa and stalked into the crowd at one point to bring a baby dressed as a construction worker briefly on stage.

"Oh so cute, give me that baby!" said the 70-year-old mogul.

He criticized the commanders who have handled the military operation, backed by U.S. air power, to recapture the northern Iraq city of Mosul from militants in scathing language unheard of from any other presidential candidate.

"What a group of losers we have," he said.

Supporters held up "Hispanics for Trump," "Women for Trump" and "blacks for Trump" at the Tampa rally, but his campaign has struggled to win any meaningful support from minority groups.

- 'Glass ceiling to crack' -

CNN reported Saturday that early turnout among Latinos in Florida was up 129 percent on 2008, statistics that are thought to favor Clinton. US media says more than 33 million Americans have already voted.

"Get out and vote! God bless you!" was Trump's parting shot.

Clinton spent Friday in the Rust Belt, a section of America that has been crushed by the decline in manufacturing, and where blue-collar Democrats are being swayed by Trump's promise to bring back jobs from China and Mexico.

She spoke at the Beyonce and Jay-Z concert in Cleveland, Ohio, a state that Obama won in 2012 but where she trails Trump by around five percentage points in the polls.

Clinton portrayed her campaign to become the first female US president as the next step in the civil rights struggle.

"We have unfinished work to do, more barriers to break, and with your help, a glass ceiling to crack once and for all," she declared, to loud cheers.

"The world looks to us as a progressive country that leads change," Beyonce said wearing a version of Clinton's trademark pant suit.

"I want my daughter to grow up to see a woman lead our country. That is why I'm with her."

In a campaign first, Trump delivered the Republican Party's weekly radio address Saturday, urging listeners to vote Republican down the ballot to elect a Republican-majority Congress.

Trump has had troubled relations with Republican leaders, many of whom withdrew their public endorsement of his candidacy after an "Access Hollywood" tape emerged in which he boasted in vulgar language about groping women.