It comes as the New York Police Department (NYPD) said the man threw pamphlets in the air before setting himself alight in a designated protest area for pro and anti-Trump demonstrators.

Police have identified the man as Maxwell Azzarello, in his mid-30s, from St. Augustine in Florida.

The NYPD said it has opened an investigation after its officers responded to the fire at around 1:37pm local time (6:37pm UK time).

The force added that Mr Azzarello has been taken to hospital and is in a critical condition.

It comes after jury selection for Trump's hush money trial concluded with 12 people, and six alternatives, chosen to decide whether the former US president covered up payments to women who alleged they had affairs with him.

Footage shared on social media shows Mr Azzarello lying on his back on the pavement outside the courthouse while the lower part of his body is on fire.

Another man sprays him with a fire extinguisher which appears to put the fire out.

Police officers are seen running over to the scene as the fire is extinguished.

The former US president was preparing to leave the courthouse before the man set himself on fire.

Freelance photojournalist Ed Quinn was outside the court at the time and told Sky News' US partner network NBC News: "I heard someone scream 'He's going to light himself on fire!'.'

"I see him dumping gasoline on his face, very deliberately.

"He had a grey T-shirt on. It soaked his face. It soaked his shirt. Boom, he went up."

Mr Quinn said it took the police about a minute to arrive.

He continued: "Women were begging, screaming, put it out, put him out."

Trump facing multiple charges in historic trial

In what is the first criminal trial of a US president, Trump is accused of criminally altering business records to cover up a $130,000 (£104,200) payment to adult film actress Stormy Daniels, real name Stephanie Clifford, during his 2016 election campaign.

Ms Daniels and former Playboy model Karen McDougal, who was paid $150,000 (£120,000), both claim to have had affairs with Trump.

HIs lawyers say the payment was meant to spare himself and his family embarrassment not to help him win the election.

Trump is facing 34 felony counts of falsifying business records and could get up to four years in prison if convicted.

He is also facing three other criminal cases that could go to trial.

He has pleaded not guilty to all charges.

Emotional juror asks to be excused

In court today, one prospective juror was excused after saying she suffers from anxiety and felt she could struggle to be impartial, while another was called to the judge's bench after bursting into tears.

The first woman said she takes medication and that as the days go on, "don't think I will be able to be completely fair".

The second broke down crying and, according to Sky News' partner NBC News, said: "I have to be honest, I feel so nervous and anxious right now. I'm sorry."

"I thought I could do this... I don't want you to feel like I've wasted anyone's time," she added before being called to the bench and excused.