A 13-year-old boy was taken to hospital for treatment after the incident in Chapel Road at around 5pm on Sunday (March 13).
Sussex Police confirmed it was called to an 'alleged stabbing' and five people were detained.
Officers armed with guns arrived at the scene on Sunday evening and members of the public were advised to avoid the area. There was said to be no threat to the wider public.
The investigation is continuing today (Monday).
Pictures taken in Liverpool Gardens show a heavy police presence, with officers searching the area, using drones.
Sussex Police has been approached for further information.