A 30-strong mob of Italian football fans have stormed into a restaurant used by Arsenal supporters, smashing windows, breaking chairs and injuring at least one person.
Witnesses described how the men, described as Napoli fans, had team scarves tied round their faces and started shouting in Italian at those inside the busy restaurant.
One worker at the Piebury Corner eatery described how they had to duck for cover and how one customer had been attacked with a belt leaving "blood all over the floor".
The London Ambulance Service confirmed a man in his 40s was taken to hospital with head injuries, that were not thought to be serious.
The gang attacked ahead of the Champions League clash between Arsenal and Napoli at the Emirates Stadium.
Emily Gould, who works at the Piebury Corner on Holloway Road, north London, said around 50 customers were inside the restaurant when a 30 rival supporters stormed the building.
She said: "I think they were Italian men with Napoli colours and scarves tied around their faces.
"They were shouting something in Italian, chanting and causing trouble down the street.
"Then then came in to the shop. I was terrified. They started swinging belts around.
"The customers were very frightened."
Piebury Corner owner Paul Campbell said the attack was "completely unprovoked". The restaurant has had to close due to the damage caused.
He said: "We have had Napoli fans inside all day today, they have been having a good time and not bothering anybody at all. They have been no problem.
"Then we had a minority of them come in, being violent, picking up chairs and tables.
"There were three girls sat near me and these thugs just came in and grabbed the chairs from under the girls.
"It was completely unprovoked, I think they just picked us at random because they saw a busy restaurant and they wanted to fight someone - anyone."
Mr Campbell said he had no reason to suspect any trouble from Napoli fans before kick-off.
He said: "We are popular with home fans and the travelling European fans too. This just came from nowhere."
The Metropolitan Police described the incident as "football-related".
A spokesman said a man had been arrested in the area for a public order offence, unconnected to the damage at Piebury Corner.
In November, Tottenham fans were injured in an attack at the Drunken Ship pub in the centre of Rome ahead of a Europa League Match between Spurs and Lazio.
Violence broke out when 50 assailants, armed with knives and baseball bats with their faces covered by motorbike helmets and scarves, stormed the bar where Spurs fans were gathered.
Ashley Mills, a Tottenham fan who was in Rome to watch the Lazio game, suffered serious injuries to his skull and thigh.
He needed emergency surgery after he was slashed in the upper thigh and lost several pints of blood.
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