UPDATE: A youth custodial officer has been hospitalised after an assault at Banksia Hill Detention Centre.
A spokeswoman for the Department of Corrective Services confirmed a male staff member was assaulted by an inmate this morning.
"The injuries have actually been assessed as not serious, but he has been taken to hospital just to make sure," the spokeswoman said.
"Any assault is considered serious."
Police were called to the centre to investigate.
A spokesman for the Community and Public Sector Union said the assault happened about 9.40am.
"There was one youth custodial officer escorting four detainees back to the Harding C unit," he said.
"It's understood one of the detainees has pulled a flexible, plastic hose from his pants and struck one of the officers on the back of the head several times.
"Apparently it was like a hose you'd have on the back of your washing machine."
The spokesman said only one detainee was involved in the assault.
Shadow Corrective Services Minister Paul Papalia said he was told the officer was struck over the head several times with an object.
"I received notification that an officer was hit over the head several times by an object and was being treated on site," he said.
"Getting hit over the head several times with an object sounds pretty serious."
Mr Papalia claimed the closure of Rangeview Remand Centre had created a more dangerous working environment for staff at Banksia Hill.
"This comes only a week after three cells were damaged there - the same week there was a riot in Albany and a murder at Wooroloo," he said.
"The system is overcrowded despite what the government says."