Sussex Police made six arrests after two men were stabbed outside JD Sports, Brighton, at 4.30pm on Monday (June 12).
The victims aged 19 and 20, and from London, were taken to the Royal Sussex County Hospital with puncture wounds, police said.
Police said a knife was recovered at the scene - outside Churchill Square Shopping Centre on Western Road - and added that the incident was not terrorism-related.
The 19-year-old underwent surgery and remains in hospital in a stable condition. The 20-year-old was treated and released.
A 21-year-old Croydon man, and an 19-year-old man, 20-year-old man and a man aged 18, all from Southwark, London, were detained on suspicion of causing grievous bodily harm and are currently in custody.
A 18-year-old man and a 24-year-old man both from Brighton who were initially detained were released without charged.
The investigation is ongoing.