Sussex Police said emergency services were called to the premises in Lydd Road at around 10.50pm on Friday (5 August) following reports of an altercation involving a group of people.
A 53-year-old man was pronounced dead at the scene during the early hours of Saturday morning (6 August). His next of kin have been informed.
The force confirmed six people have since been arrested on suspicion of murder and remain in custody.
Detective Superintendent Jon Hull said: “Our investigation is at a very early stage, but I would like to reassure the public that this appears to be an isolated incident with no wider risk of harm.
