Police came under a hail of bricks and eggs after trouble flared at a Tommy Robinson campaign rally, authorities have said.
Two vehicles were damaged by the makeshift missiles as counter-protestors clashed with supporters of the far-right MEP in Oldham on Saturday.
The objects were thrown as a line of officers attempted to keep the two groups separate in the town's Limeside area.
Now, Greater Manchester Police has warned arrests will follow the disturbance,
Chief Superintendent Neil Evans said: “Those involved can expect to be arrested and dealt with robustly.”
He added: "Everyone has the right to free speech and we will always do our best to facilitate this so people can exercise this right in a safe environment.
“This evening, people took advantage of this and turned to violence, throwing objects including eggs and bricks. We understand that many of those involved were not from Oldham. Whoever is responsible, this behaviour will not be tolerated."
The force said the incident itself had been brought to a close by the late afternoon, and that rumours that someone had been stabbed had been found to be false.
A video posted on Facebook by a group calling itself the Muslim Defence League showed a large number of men shouting at Robinson’s supporters across the police blockade before they begin throwing indistinct objects..
A separate live video shared on YouTube by Danny Tommo, a known associate of Robinson, appeared to show the same clashes from the other perspective. In the clip, it is claimed bricks are being thrown.
Chief Superintendent Evans said: "Police officers responded quickly to the disorder and dispersed those involved. Fortunately, no-one was seriously hurt and damage was only caused to vehicles.
“Now the incident has come to a close and people in the area have dispersed, our attention turns to the investigation into the circumstances that surround it."
Robinson, whose real name is Stephen Yaxley-Lennon, turned up in Limeside as part of his bid to be elected to the European Parliament as an independent representative for the North West region.
But it not the first time his campaign has run into controversy.
Scuffles and low turn-out have dogged his appearances in towns across the region. In one now famous incident, the 36-year-old – who has a string of criminal convictions – had a milkshake thrown over him. In another, he was filmed canvassing a Salford woman pushing a pram who gives him especially short shrift. “You’re spouting any old shite,” she tells him.
Writing on Twitter about Saturday's clashes, Jim McMahon, Labour MP for Oldham West and Royton, said: "It's horrible to see our town being used for hate and division when our own future is a shared one, long after the circus has left town.
"Very different from our own stall in Oldham earlier today where we celebrated our town."
Alongside the words, he posted a video, adding: "We don't need people, coming to our town, trying to divide us for their own political agenda.
"We need to come together and be the best Oldham we can be."