A witness described seeing “15 or 16 police cars, eight ambulances and two or three riot vans” respond to the “riot call” to Curzon Ashton’s Tameside Stadium.
Eight men were arrested on suspicion of public order offences near the sixth-tier Vanarama North club ground after protesters descended upon the Eritrean Cycle Festival.
It was reported the group were taking part in an organised protest against the Eritrean government in east Africa.
A number of objects were thrown and people were attacked in what police have called “an appalling act of violence”.
Another witness told Mirror Online a group of about 20 men, who had hired out a function room at the football club, were allegedly attacked by a “rival” group as a ‘protest erupted into violence’.
It is believed up to 40 people were involved – 20 on each side.
“People are insisting that a very serious attack took place,” the witness said.
A spokeswoman for North West Ambulance Service said children were among the 12 people treated by paramedics at the scene.
All suffered minor injuries apart from a 46-year-old woman, who was taken to Tameside General Hospital, suffering a cut not believed to be serious.
Two teenage girls, aged 14 and 17, were among those who suffered minor injuries.
Chief Inspector Andy Harty, of Greater Manchester Police, said: “The vast majority of people attending the event today were innocent people, including children, who sadly got caught in the middle of this appalling act of violence.
“Following the fast work of officers a number of men were arrested at the scene and we will continue to question them as this investigation progresses.
“However, we are still in the very early stages of inquiries and we are keen to hear from anyone who witnessed this incident.
“In particular we would like people to come forward with phone or dash-cam footage that could be vital to finding all those responsible.
“This type of behaviour is completely unacceptable and I want to assure the residents of Tameside that we are doing everything we can to bring any offenders to justice.”
The eight men arrested are being questioned in custody, police said.
The Eritrean Cycle Festival was happening at the complex today and was due to run until Sunday, but has now been called off.
People at the festival told the Manchester Evening News that protesters ‘stormed their party and started attacking those present’.
An organiser told Mirror Online he is “not sure” if the disturbance was connected to the festival.
“There were some guys there that came and disturbed things,” he said.
“I don’t know what the issue was.”
Organisers stressed the event was nothing to do with the Eritrea government and was set up to celebrate road cyclists who had represented the nation for years.
An earlier statement from Greater Manchester Police said: “At around 3.15pm today (Saturday 16 June 2018) police received reports of a large disorder at Tameside Stadium.
“Officers attended and a number of people were arrested at the scene. Several people are believed to be injured.
“Officers are currently working to understand the circumstances and enquiries are ongoing.”
A witness said they saw ’15 or 16 police cars converge on a riot call’.
They said: “There were about 15 or 16 police cars, eight ambulances and two or three riot vans.
“We heard one police officer say it had come through as a riot call. We just drove in but then we couldn’t get out.
“I saw quite a few people getting arrested. They were bringing people out in handcuffs. I saw a taxi driver with a bloody nose.
“It’s the first time anything like this has happened here.
“There’s usually football events but nothing like this ever happens, it’s usually quite quiet.”
The incident has happened in the vicinity of a sports complex in Ashton-under-Lyne which includes Tameside Stadium, used by Curzon Ashton FC, an athletics track and the Tameside Cycle Circuit