Two men underwent emergency surgery after bottles were smashed in their faces in a street fight.
One man suffered a cut to an artery in his neck and the other was cut to the bone in his jaw.
Both suffered massive blood loss. Last night their conditions were said to be serious.
Blood spots stain the pavements in Regency Square, Brighton, where the fight took place.
Police said the clash involved two groups of three people in their 20s, who had been socialising separately.
The groups clashed first in Churchill Square, just before 2am yesterday.
Verbal insults and punches were thrown in the adjoining Clarence Square before bottles were used in Regency Square.
Police said an Asian man was smashed in the face, cutting him to the jawbone.
A white man in the other group was then hit, the broken glass slicing an artery.
The Asian man staggered to a kebab restaurant in nearby Preston Street and an ambulance was called.
The white man and his two friends, a man of mixed race and a woman from China, were spotted by police minutes later at the junction of Western Street and Kings Road. Officers called an ambulance.
Both victims were taken to the Royal Sussex County Hospital.
Two people were arrested and two more were being hunted by police last night.
Detective Inspector Ian Pollard said: "We do not believe this incident was racially motivated but it was an extremely violent incident and we need to bring offenders to justice.
"I would urge anyone who witnessed the attacks or may know where these people were earlier in the evening to come forward."
The north end of the square was taped off yesterday morning.
Forensic experts were combing the scene for clues while officers carried out house-to-house inquiries.
One resident, calling himself Michael, said: "This was terrible. We get a few problems in the square and you sometimes hear screams late at night but there's been nothing like this that I can remember."
A spokeswoman for Brighton and Hove police said: "We are trying to establish where these two groups were earlier in the evening, whether they had been drinking and what started the argument."
Anyone with information should call Brighton CID on 0845 6070999.
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