Community and Public Sector Union representative Julian Kennelly said staff were on site on Thursday, but stopped work under Occupational Health and Safety laws.

It comes after two staff members were allegedly attacked at the centre on Wednesday night.

One 28-year-old man was taken to hospital in a stable condition with upper body injuries.

Mr Kennelly said one staff member, who had only been at the facility for three weeks, was allegedly assaulted by two offenders.

Mr Kennelly said the man's keys and swipe card were stolen.

The offenders allegedly escaped the unit, got up onto a shipping container, and over the fence to another yard.

Security staff, Mr Kennelly said, eventually stopped the two offenders with capsicum spray.

The Department of Justice and Community Safety confirmed an incident took place but did not go into more detail.

"The department takes the safety and security of all staff seriously and the matter has been referred to police," the department spokesperson said.

"Violent behaviour or assaults at youth justice centres are absolutely unacceptable. New laws are now in place that strengthen the consequences for young people who assault custodial workers, damage property and escape or try to escape.

"This includes a presumption that, if convicted, they will serve their sentence on top of any other period of detention."

Police say they are investigating an alleged assault at the centre.

Union representative Mr Kennelly said a female staff member was also set upon in another part of the centre around the same time on Wednesday.

He said two other offenders tried to take the woman's keys and swipe card.

Mr Kennelly said they failed due to the early response from security guards. The woman was able to go home uninjured, but was reportedly traumatised by the incident.