Detectives are investigating two separate attacks in Norwich's night life area last night.
An attack on Prince of Wales Road has left one man in the Norfolk and Norwich University Hospital with serious head injuries.
A number of people remain in custody at Wymondham Police Investigation Centre.
Meanwhile, a man in his 20s suffered a fractured cheekbone in a separate incident in Riverside Road.
Officers were called to the area, near to the junction with Prince of Wales Road, shortly after 1.10am following reports a man was unconscious.
Officers are continuing to investigate and the area was cordoned off until 9.20am while officers carried out inquiries.
Anyone with information concerning either incident should contact Norwich CID on101.