Donald Trump has denied dozens of criminal counts of willfully mishandling US government secrets and scheming to prevent their return, in a historic first appearance in federal court.

Trump appeared on Tuesday before a judge in Miami to be formally presented with 37 charges brought by the government following a special counsel probe that opened after an FBI raid of his Florida mansion last August.

"We are certainly entering a plea of not guilty," Todd Blanche, his attorney, told the hearing.

It was the former president's second arraignment as he battles a deluge of legal threats, coming just 10 weeks after he was charged with a string of felonies in Manhattan over hush money payments to an adult movie star.

Earlier, Trump surrendered to face federal charges of mishandling US government secrets — the latest and most serious in a string of probes threatening his bid to win back the White House.

"One of the saddest days in the history of our country. We are a nation in decline," Trump posted on his Truth Social platform as he was driven to court, repeating his regular accusation of a "witchhunt!"

Dozens of Trump supporters gathered nearby as the 1900 GMT court appearance approached, some wearing "Make America Great Again" baseball caps and one with a sign reading "Indict Jack Smith" — the special prosecutor who brought the charges.

A judicial source said Trump will be processed like other defendants. He will have his fingerprints taken digitally and a photo of him will be uploaded into the court records but not released to the public.

Police, including some on horseback and bicycles, were out in force braced for protests and the possibility of unrest, but the atmosphere was festive with a local radio station blasting Cuban salsa music.

Trump headed back to his golf club in Bedminster, New Jersey, to deliver an evening speech protesting his innocence — but not before stopping to greet supporters at a Cuban restaurant in Miami's Little Havana, where they sang happy birthday in his honour.

"We have a country that's corrupt," Trump told the gathering, railing at the charges brought against him.

"A country in decline like never before," he said. "I think it's a rigged deal here."

Earlier, Trump, who made the 25-minute trip from his Doral golf course to the courthouse in a motorcade of at least six black SUVs, earlier lashed out at Smith on Truth Social, calling the prosecutor a "thug" and a "lunatic."

Trump is facing 31 counts of unlawfully retaining classified documents after leaving the White House in 2021, punishable by up to 10 years in prison, conspiracy to obstruct justice, making false statements and other offences.

The rebellious Republican said he would plead not guilty but make no statement from the courthouse after the hearing.

"I'll just say not guilty," Trump told conservative radio host Howie Carr late Monday.

"I did nothing wrong. Presidential Records Act, it's not even a criminal event. There is no criminality here. It's ridiculous."

'Dumbfounded'

Trump, who turns 77 on Wednesday, is accused of willfully hoarding dozens of classified documents he took unlawfully to his beachfront mansion in Florida, refusing to return them and conspiring to obstruct investigators seeking their recovery.

He is also accused of sharing sensitive US secrets with people who had no security clearance.

Lazaro Ezenar, 48, was among those who turned out to back the former president.

"I can't believe he's going through this again," Ezenar told AFP, referring to the criminal charges brought against Trump in a hush-money case in New York — a first for a former US president.

"This is historic and I'm just dumbfounded that, as a country that is a beacon to the world, I have to see this show that is disgracing what America represents."

The runaway frontrunner in the 2024 Republican primary has vowed to stay in the race regardless of the outcome of the documents case.

The 49-page indictment, dismissed by Trump as "ridiculous," includes photographs showing boxes of documents stacked at Mar-a-Lago, his Palm Beach residence, in a ballroom and in a bathroom and shower.