Former US president Donald Trump has pleaded not guilty to 34 felony counts of falsifying business records.

The plea came during a brief arraignment in a New York courtroom as Mr Trump faced a grand jury indictment arising from a hush money payment to a porn actor during Mr Trump’s 2016 campaign.

Judge Juan Merchan warned the former president to refrain from rhetoric that could inflame or cause civil unrest.

Judge Merchan also warned Mr Trump that he could be removed from the courtroom if he was disruptive, but Mr Trump spoke only a few times to respond to questions.

The arraignment, though procedural in nature, amounts to a remarkable reckoning for Mr Trump after years of investigations into his personal, business and political dealings.

Any alleged offence punishable by more than one year in prison is called a felony in the US justice system.

The case is unfolding against the backdrop not only of his third campaign for the White House but also against other investigations in Washington and Atlanta that might yet produce even more charges.

A silent and stony-faced Mr Trump entered the courtroom shortly before 2.30pm local time without saying anything.

Minutes earlier, he narrated his feelings in real time, describing the experience as “SURREAL” as he travelled from Trump Tower to lower Manhattan to face a judge as the first former president in American history to be criminally prosecuted.

Wearing his signature dark suit and red tie, Mr Trump turned and waved to crowds outside the building before heading inside to be fingerprinted and processed.

Mr Trump, who was impeached twice by the US House but was never convicted in the US Senate, is the first former president to face criminal charges.

Mr Trump is scheduled to return to his Palm Beach, Florida, home, Mar-a-Lago, on Tuesday evening to give remarks. At least 500 prominent supporters have been invited, with some of the most pro-Trump congressional Republicans expected to attend.

A conviction would not prevent Trump from running for or winning the presidency in 2024.

The investigation is scrutinising six-figure payments made to porn actor Stormy Daniels and former Playboy model Karen McDougal. Both say they had sexual encounters with the married Mr Trump years before he got into politics.

Mr Trump denies having sexual liaisons with either woman and has denied any wrongdoing involving payments.

He is next due in court in December, but his lawyers asked for him to be excused from attending the hearing in person because of extraordinary security proceedings.