Two people are in hospital today after assaults in Marine Parade and Western Row last night that police believe were linked.
One has suffered a serious head injury and the other has cuts and bruises.
An area of the seafront and a property in Marine Parade was taped off this afternoon as enquiries continued.
A number of people are in custody helping police with enquiries.
A spokesman from Sussex Police said: “This is a complex case and because of the different sites and the links between the people, investigations are still being made.
“Police were called to a property on Marine Parade last night and a man was found injured in a beach shelter at around 4am this morning.
“We believe the two fights were linked and are appealing for witnesses.”