Mr Biden told supporters: “You hold the power. If Florida goes blue [Democratic], it’s over.”
Celebrating soaring economic figures, Mr Trump, a Republican, said of his rival: “He’s going to lock you down.”
With just five days to go until election day, Mr Biden has a solid lead nationally in opinion polls.
But his advantage looks less assured in the battleground states, such as Florida, that will decide who ultimately wins the White House.
More than 81 million people have already voted, 52 million of them by mail, setting the US on course for its highest electoral turnout rate in more than a century.
Trump warns of ‘crippling’ Biden depression
At Thursday’s rally in Tampa, Mr Trump revelled in a new federal projection that the US economy had expanded at an unprecedented 33.1% annual rate in the most recent quarter, following a record 31% contraction in the previous three months during the coronavirus crash.
Florida is a must-win for Mr Trump and a key opinion poll average shows him just 1.4 points behind Mr Biden, which amounts to a statistical dead heat.
At a 100-minute outdoor rally, Mr Trump told thousands of people, many of them crowded together without masks: “Joe Biden’s plan is to deliver punishing [coronavirus] lockdowns. He’s going to lock you down.”
“Look, we were compared to Europe,” noted the president. “‘Germany is doing so well, France is doing so well, everyone’s doing so well.’ No, they’re not doing well.”
While emphasising Europeans were allies, he continued: “They’re spiking up big, they’re shutting down, they’re locking down.
“I disagree with that because we’re never going to lock down again. We locked down, we understood the disease and now we’re open for business.”
The president was introduced by First Lady Melania Trump, making a rare appearance on the campaign trail. Her biggest applause line came when she said: “We are a country of hope, not a country of fear or weakness, and we have a leader who shows us that every single day.”
Mr Trump had been due to hit another key state, North Carolina, on Thursday evening, but cancelled that event in Fayetteville because of foul weather from Tropical Storm Zeta in the area.
The storm reportedly disrupted early voting in another election battleground, Georgia, sparking power cuts in some precincts and toppling trees that blocked off mobile polling sites.
Mr Trump – who began this month in hospital with coronavirus – is visiting 10 states in the last week of the campaign and will host 11 rallies in the final two days, a campaign official said.
The president is hoping that media coverage of his rallies will compensate for his chronic deficit in ad spending as a result of his now-limited campaign coffers.
In Florida alone, according to data from ad tracking firm Kantar/CMAG, Mr Biden and his allies are outspending Mr Trump by more than three to one.
But in a potential boost for Mr Trump, on Thursday he won a rare thumbs-up from an African American celebrity, rapper Lil Wayne, who appeared to endorse him.
Biden: Trump has ‘given up’
In a 23-minute appearance, Mr Biden spoke at a drive-in rally at a college in Broward County, north of Miami, on Thursday.
“I do miss the opportunity to just wander in and shake hands with all of you, but we decided a while ago that we were going to try to be responsible,” he said.
He thanked attendees, many of whom remained by their cars to avoid possible spread of Covid-19, for wearing masks and practising social distancing.
Mr Biden dismissed Mr Trump’s rally on the other side of the state as a “superspreader” event.
“Donald Trump has given up,” he said, of the coronavirus pandemic. The US is currently seeing a record rate of infection, and is nearing nine million confirmed cases.
Mr Biden urged a national mask mandate, crying: “This is not a political statement, it’s a patriotic duty, for God’s sake!”
The Democrat said he would not lock down the country as president, though he did not rule it out at a debate last week.
Mr Biden described his rival as “a person who knows the only way he can win is if he divides us on race, nationality, national origin, gender”.
He added: “Look, everybody knows who Donald Trump is. We got to show him who we are.”
Mr Biden also pitched directly to Hispanic voters, as polls show Mr Trump is making gains with Latinos, a vital voting bloc in Florida and other battleground states like Nevada.
“President Trump can’t advance democracy and human rights for the Cuban people or the Venezuelan people, for that matter, when he has praised so many autocrats around the world,” Mr Biden said.
Mr Trump swiftly hit back on Twitter, saying: “Our opponents want to turn America into Communist Cuba or Socialist Venezuela.”
On Friday, the two rivals will hold another set of duelling rallies, this time in Minnesota. It is one of the few Midwestern states that voted for Hillary Clinton in 2016 and the president is hoping to flip it this time.
Mr Biden will also campaign in Wisconsin and Iowa on Friday. On Saturday, he will hold a joint rally in Michigan with former US President Barack Obama, whom he served as vice-president.