Manchester United's fixture postponed after fans storm the pitch. ITV News Correspondent Chris Skudder reports from Old Trafford
A police officer has been left seriously injured as Manchester United's game against Liverpool was postponed after fans stormed the pitch at Old Trafford ahead of kick-off.
Protesters also gathered outside the ground and, police say, began to throw bottles, ‘significantly slashing’ one officer’s face.
The scenes have been condemned as "completely unacceptable" by police representatives.
Stu Berry, chairman of the Greater Manchester Police Federation, said officers are not "punchbags for people protesting" a cause.
He added: "At the end of their shifts, hard-working police officers should be able to go home to their families in one piece. Not be rushed to hospital."
He said the culprits must be identified and prosecuted because football fans do support peaceful protest in favour of the national game but these were "appalling scenes" of "mindless violence" that was carried out by a "minority" of people.
In announcing the postponement of the match, Manchester United said while they accepted the right of their fans to protest peacefully, they regretted "the disruption to the team and actions which put other fans, staff and the police in danger".
The club said in a statement: "Following discussion between the police, the Premier League, Trafford Council and the clubs, our match against Liverpool has been postponed due to safety and security considerations around the protest today. Discussions will now take place with the Premier League on a revised date for the fixture.
Speaking on Good Morning Britain, Ian Stirling from Manchester United Supporters Trust says "football is in danger"
Thousands of fans stage protest outside Old Trafford
"Our fans are passionate about Manchester United and we completely acknowledge the right to free expression and peaceful protest.
"However, we regret the disruption to the team and actions which put other fans, staff and the police in danger. We thank the police for their support and will assist them in any subsequent investigations.
A Greater Manchester Police spokesperson said: "Officers were aware of a protest planned to take place in Old Trafford today and were working closely alongside partners to ensure those that attended were kept safe whilst enabling their right to peaceful protest.
"Early this afternoon, groups of protestors began to gather at Old Trafford and separately at The Lowry Hotel, Salford where the United players were staying. By late afternoon around 200 protestors had gathered outside the Lowry and over 1,000 at Old Trafford.
Reporting from outside Old Trafford, ITV News correspondent Chris Skudder looks at the impact the protests could have on the clubs
"Officers continued to closely monitor the situation, engaging with those present but as the groups grew in size; it became clear that many of those present were not intending to exercise their right to peaceful protest. Flares were let off and bottles thrown at officers.
"Protestors outside Old Trafford became especially aggressive and antagonistic towards police before a group of about 100 forced entry to the ground with some United staff having to lock themselves in rooms.
"Those in the stadium were evicted by officers but outside on the forecourt hostility grew with bottles and barriers being thrown at officers and horses. Two officers have been injured with one officer being attacked with a bottle and sustaining a significant slash wound to his face, requiring emergency hospital treatment.
"With the situation increasing in hostility, additional officers had to be deployed and officers had to be drawn in from neighbouring forces to assist Greater Manchester officers.
"Following discussion with The Premier League, Trafford Council and the clubs, a joint decision was made to postpone the match for safety reasons."
Video from @Gezz_MUFC on Twitter.
United supporters were expressing their anger following plans backed by the Glazer family to join a proposed European Super League, which collapsed soon after.
Red fences put in front of the East Stand did not last long, being quickly toppled as stewards were overawed and chanting supporters made their way towards the tunnel.
It is believed those who gained access to the ground did so via the Munich Tunnel, after pushing down barriers, despite the attempts of security guards to prevent that happening.
A large number of fans ran back out of the stadium complex at around 2.20pm.
These fans say the protest will make a "real statement" to the club.
Earlier, hundreds of Manchester United fans have surrounded the football team's bus outside The Lowry Hotel in Salford to protest against the football club's owners.
Video from @Cantona_Collars on Twitter.
Supporters could be seen gathering outside the hotel where the players are due to leave from for their game against Liverpool.
The protests follow the debacle of the European Super League in April. Over 1,000 fans gathered outside Old Trafford last Saturday (April 24) with banners calling the Glazers 'greedy' and 'selfish' brandished outside the East Stand.
Joel Glazer had been named European Super League vice-chairman when the announcement was made, but he apologised in a letter to Manchester United fans after the club pulled out of the plans the day before.