Rival gangs brandishing hammers and machetes clashed on the streets of Accrington.
Around 20 Asian men are believed to have been involved in fought middle of a main road on the outskirts of the town centre.
A 36-year-old man suffered a broken jaw after being clubbed to the back of his head with a hammer during the brawl at around 10pm on Saturday.
Shocking CVTV images of the fight show hooded figures squaring up before the gangs fled as police moved in.
Witnesses described the clash as 'something you would see in America' and some said violence had been brewing at either end of Blackburn Road all day.
Detectives have made three arrests but said they don't know why the violence had taken place.
Detective Inspector Jill Johnston said the brawl may have been pre-planned.
She said 10 extra officers were sent out on patrol in the town centre and surrounding areas following the fight.
DI Johnston, of Accrington CID, said: “For that many men in their 20s and 30s to be fighting in the street, not near a pub or nightclub, is rare.
“Whether it is two groups who have arranged a fight, I don't know.
“It is possibly a dispute between two local Asian families or groups. They are old enough to know better.”
She added: “We are trying to make some sense of it all. We have CCTV footage of the incident. It appears that one group has gone to the scene in vehicles and then entered into a fight.
“We are trying to piece it all together and are hoping to make some more arrests.”
The incident took place at around 10pm on Blackburn Road in Accrington, close to Swiss Street.
Residents said traffic was held up as the gangs fought in the road.
When the police arrived the men all made off.
One businessman, who asked not to be named, said: “It was lads from the top and bottom ends of town.
“There was about 20 lads - some were in cars and were ramming people on the road.
“It looked like a gangland and is a big concern as I live and work around here with my family.”
He added: “They started clashing and waving hammers and machetes around like crazy.
“It was just mad and was going on though the whole day with little clashes. It just came to a head and ended in a big me-lee.
It was something you would see in America.”
One Blackburn Road resident, who declined to be named, said more cameras and street patrols are needed.
He said: “We don't know who they were or what it was about. It's very worrying when something like this happens near your home.”
Any witnesses can contact Accrington CID on 01254 353741.
*Three men from Accrington were arrested on Tuesday morning, aged 22, 23 and 24. They have since been released on police bail.