Masked thugs invaded a talk organised by a university free speech society last night before setting off smoke bombs and attacking security guards.

The self-proclaimed 'antifascist' protesters forced their way into the King's College London lecture hall and grabbed the speakers' microphones before smashing windows and leaving notes threatening the moderator.

Several security guards were punched and had to go to hospital, according to the organisers, who were forced to evacuate the building and call the police.

Shocking footage showed fights breaking out between the protesters and members of the audience with several punches being thrown at the event at King's College London last night

Footage showed fights breaking out between the protesters and members of the audience with several punches being thrown.

An onlooker, who was waiting outside the hall when the gang vaulted the barriers, described the moment the mob launched an unprovoked attack on security guards.

'Ten to 15 people dressed all in black, with black hoods and black face masks, leapt over the barriers and instantly engaged in a fight with two or three security guards,' he said.

'They tried to stop them but they just started punching them in the face. One guard, a grey-haired gentleman who looked to be in around 60, received several punches.'

A protester raises his arm as he is restrained by a security guard

Last night's event was organised by the KCL Libertarian Society and featured Ayn Rand Institute director Dr Yaron Brook alongside controversial YouTube personality Sargon of Akkad, real name Carl Benjamin.

Mr Benjamin identifies as a 'classic liberal' but has been branded by critics as a member of the 'alt-right'.

War studies student Eberle Miller, 21, who watched the chaos unfold, told MailOnline: 'The protesters hospitalised several university security guards, smashed the window of a grade-one listen building and threw smoke bombs.

'It only proves they are incapable of persuading anyone to their side through reasoned discourse.'

KCL students' union ordered the Libertarian Society to reschedule last night's talk from March 4 because they claimed security could not be guaranteed on a weekend.

And on the night itself KCLSU officials prevented non-student members of the public who had previously booked tickets from entering for security reasons.

The Libertarian Society, which campaigns against the students' union's safe space policy as a threat to free speech, criticised the hard-Left protesters and student officials for the violence.

A damage door outside the lecture hall where masked thugs forced their way into a free speech event last night

'After refusing entry to ticketed members of the public for 'safety' reasons, the King's College London & KCLSU administration failed to prevent violent and masked activists storming the stage and the university at tonight's event,' it said in a statement.

'Windows were smashed and gas bombs lit outside campus. A number of KCL security guards were on their way to hospital after being assaulted.

'The event was cancelled and evacuated after threats to the moderator. This was an act of violence, clearly intended to silence Yaron and Sargon's planned debate, via a series of jackbooted totalitarian tactics that unfortunately proved successful tonight.'

A number of threatening notes were left by protesters, who waved an 'Antifa' [anti-Fascist] flag.

One read: 'The guy moderating the talk is on my course and he'll have a difficult time once the strike is over.'

The Metropolitan Police confirmed they had attended the event but said its officers had not heard of any injuries. Pictured: A protester holding an 'anti-Fascist' banner

The Metropolitan Police confirmed they had attended the event but said its officers had not heard of any injuries.

'Police were called at 6.50pm on Monday, 5 March to reports of a disruption at King's College, Westminster,' a spokesman said.

'A group of people are believed to have forced their way into a building and set off fire alarms and a smoke bomb.

'The group were had dispersed by the time police arrived. There have been no reported injuries. No arrests. Enquiries continue.'

Event chair Danny Al-Khafaji said: 'This was an explicit attempt by those opposed to the free exchange of ideas and rational debate, to undermine the principle of freedom of speech.

'We will not be deterred from fighting against the authoritarian nature of safe spaces and no-platform policies. We believe freedom will prevail.'

Momin Saqib, President of KCLSU said: 'I am appalled by the acts that were perpetrated in King's College London yesterday evening.

'I strongly respect and encourage the right to freedom of speech, the right to challenge each other and the right to peaceful protest.

'It is unfortunate that the event was marred by violence by people who took an extreme and an unacceptable approach.'

KCLSU was widely criticised last year after MailOnline revealed it pays 'safe space marshals' £12-per-hour to police talks deemed 'risky' by its officials.

They monitor any speaker thought likely to perpetrate a 'safe space breach', which included Tory MP Jacob Rees-Mogg - who was watched by a total of three marshals at a talk.

The officials are also required to put up posters saying, 'This is a Safe Space' and record any instances of offensive behaviour reported to them by members of the audience.