A police officer was knocked unconscious while arresting two men accused of assaulting people.
Northumbria Police said the female officer was one of two responding to reports of men punching and kicking people in Newcastle.
She was treated at hospital for head injuries and later released. Four men came to the aid of the officers at about 03:20 BST on Monday.
Two men, aged 25 and 36, have been arrested over the incident.
Northumbria Police said they received reports that two men had assaulted people on the Castle Stairs.
It said the officers were attacked near the Quayside and were helped by four Asian men.
A spokeswoman appealed for the "brave" men to come forward as they did not give their details to officers.
She added that three detention officers and a custody nurse were later attacked at Forth Banks Police Station.
The two men have been arrested on suspicion of assaulting an officer in the execution of their duty and are being held in custody.