A reveller's face was gashed during a mass brawl which broke out in Birmingham's Jewellery Quarter at 4.30am this morning (Saturday 12).
Residents were woken by shouting and violence as four men fought in St Paul's Square.
It is believed that they had been rowing in a nearby pub earlier and the fight spilled out onto the streets.
One man was treated for serious facial wounds, while the other three suffered minor injuries.
Police erected tents around the scene of the fight.
It is believed that this was necessary to cover up the pools of blood that covered the pavement as the violence broke out.
Around eight officers were investigating the crime scene yesterday morning.
One detective was spotted carrying a bag of clothes.
On man living nearby, who did not wish to be named, said: "There was a lot of noise at about 4am on Saturday. I woke up and thought there was building work going on outside until I realised the time.
"There were a lot of people shouting and there were loud bangs.
"My girlfriend went to look out the window, in case it was someone vandalising cars, but she couldn't see anything.
"She heard people saying something like come on, let's do another one."
Another resident said: "It was a gang of about five lads and they came out of one of the pubs and had a fight on the square. But it must have got a little bit serious because one of them got stabbed.
"A friend of mine lives just above where it happened and she said it was a pretty big fight."
A West Midlands Police spokeswoman said: "Officers are investigating an assault which occurred at 4.30am on Saturday involving four men. One suffered serious facial injuries during the incident. Others suffered minor injuries.
"Two men are in custody helping police with their inquiries."
The incident happened just hours after two men were stabbed to death in Birmingham city centre.
A man is being questioned by detectives following the brutal attack, in front of scores of horrified shoppers and workers in Union Street, during the busy evening rush hour.
Onlookers saw police officers and passers-by trying to revive the victims and were soon joined by medics, but they were unable to save them and both were pronounced dead at the scene.
A man was arrested outside the Odeon in New Street shortly after the attack. Police were last night unable to confirm whether the victims, both in their 30s, knew their attacker.