Last updated 10.30pm.

Donald Trump on Tuesday pleaded not guilty at a packed New York courtroom as he became the first American president to be arrested on criminal charges, which have already upended the 2024 White House campaign.

With a stern glare to the waiting press, the 76-year-old former president walked into the Manhattan courtroom for the historic hearing where he was officially slapped with 34 criminal counts.

Trump pleaded not guilty to all charges, which include the felony of conspiracy stemming from hush money paid to a former porn star during the tycoon's 2016 election campaign, to keep quiet over an alleged affair. Other charges included falsification of business records. 

He was later released from custody without any pre-trial restrictions.

The judge, Juan Merchan, said during the hour-long hearing that a trial could potentially start in January 2024, although Trump's lawyers indicated they would rather push it back to the spring.

Trump was expected to speak at length later including at a campaign-style event after the native New Yorker flies back to his estate in Florida.

In a spectacle playing out on live television -- with rival protesters rallying outside -- the hearing marked a watershed moment for the US criminal and political system the year before an election in which Trump leads the race to be the Republican nominee.

"Seems so SURREAL -- WOW, they are going to ARREST ME," Trump posted on his Truth Social app as he headed to the courthouse from Trump Tower, where he spent the night before the hearing.

"Can't believe this is happening in America. MAGA!"

The twice-impeached Republican claims he is the victim of "political persecution" -- but is also using the court case to energize his support base and raise millions of dollars for his bid to reclaim the White House next year. 

"THE RADICAL LEFT DEMOCRATS HAVE CRIMINALIZED THE JUSTICE SYSTEM," Trump wrote hours before the hearing, branding the legal proceedings a "kangaroo court." 

Trump raises a fist towards the crowd as he leaves Trump Tower to head to court. Photo: AFP

Hundreds of people gathered outside the venue -- both of Trump supporters and anti-Trump demonstrators, as well as media and curious onlookers. Police lined the streets while helicopters buzzed in the skies as Trump's motorcade made the short drive to court, a journey given wall-to-wall live coverage on US networks although cameras were not allowed for the hearing itself.

Police stepped into the fray as the pro-Trump side -- many sporting "MAGA" hats and attire emblazoned with the American flag -- yelled slurs at counterprotesters.

The anti-Trump camp unfurled a large banner reading "Trump lies all the time" and chanted "Lock him up!" as Trump fans waved a flag with the slogan "Trump or Death."

Trump was not subjected to a "perp walk" -- in which a defendant is escorted in handcuffs past media cameras.

But the former president was believed to have undergone the standard booking procedure of being fingerprinted -- and potentially photographed, which would result in an all-time famous mug shot -- at the Manhattan District Attorney's office.

Trump was indicted last week by a grand jury in the case brought by Manhattan District Attorney Alvin Bragg, an elected Democrat.

The charges revolve around the investigation of $130,000 paid to adult film actress Stormy Daniels just days before Trump's election win.

Trump's former lawyer and aide Michael Cohen, who has since turned against his ex-boss, says he arranged the payment to Daniels in exchange for her silence about a tryst she says she had with Trump in 2006.

Trump, whose third wife Melania had recently given birth at the time, denies the affair. 

Trump is facing a series of separate criminal investigations at the state and federal level that could result in further -- more serious -- charges between now and election day.

They include his efforts to overturn his 2020 election loss in the state of Georgia, his handling of classified documents, and his possible involvement in the storming of the US Capitol on January 6, 2021.

Republicans have largely rallied around Trump, including his rival in the party's presidential primary, Florida Governor Ron DeSantis, who called the indictment "un-American."

President Joe Biden, mindful that anything he might say could fuel Trump's claim of a politically "weaponized" judicial system, is one of the few Democrats holding back over the indictment of his rival.

Asked Monday whether he had faith in the legal system, Biden simply replied, "Yes."