"We are going to keep America great again," the president told the Orlando event on Tuesday night, in a reworking of his familiar slogan.
US President Donald Trump has formally launched his re-election campaign, urging supporters to "keep this team in place" for four more years.
The Republican president made his case before thousands of supporters at a rally in Florida, calling the state "my second home".
Mr. Trump used the announcement to lash out at Democrats, accusing them of trying to "rip your country apart".
Early polls place Mr. Trump behind some potential Democratic challengers.
He entered the stage with his wife Melania, who said she was "excited" to be the first lady for six more years.
Senior figures from the White House, including Vice President Mike Pence and outgoing press secretary Sarah Sanders, also spoke at the rally.
"Tonight I stand before you to officially launch my campaign for a second term as president of the United States," Mr. Trump told supporters. "I promise you I will never ever let you down."
Florida is a key battleground state and one that Mr. Trump narrowly won in 2016.
"We are going to keep America great again," the president told the Orlando event on Tuesday night, in a reworking of his familiar slogan.
Some supporters had been waiting since the early hours of Monday morning to see the president.
A counter-demonstration against his appearance was also held nearby, the BBC reports.