Phil Pregnell, a United Voice delegate, claimed staffing levels at the prison had remained the same while the prisoner population increased 28 per cent in four years, placing staff and inmate safety at risk.

In the current financial year, there were 48 workers compensation claims for correctional officers, 16 of whom had returned to work.

The planned $270 million northern prison was not due to be fully operational for 10 years, with it becoming a remand centre within five.

Mr Pregnell said the system would continue to play catch-up with the prisoner population for the foreseeable future.

"There's gridlock within the prison system. Trying to get people from the remand centre into prison, and moving them to courses and training, and into courts, it's a struggle on a daily basis," he said.

"It's already too late, the infrastructure should have been in place now.

"There was no forward planning. We are in a position where we do not have the infrastructure in place for the number of people coming through the courts."

More on Tasmania's prison system: Cycle of offending: Housing crisis leaves prisoners on the street

Single rooms have become doubles, and double rooms have become triple to handle the growing prisoner population at Risdon, Mr Pregnell said, meaning volatile prisoners who are prone to violence are almost permanently around others.

There were 90 victims of assault in Tasmanian prisons from July last year to April this year. Of those, 12 were serious assaults resulting in hospitalisation and 49 were injured as a result of a fight.

Nineteen Corrections staff had been injured as a result of assaults during the same period.

The government has consistently disputed union claims about the cause and significance of partial lockdowns at Risdon.

United Voice carried out stop-work action among Corrections staff last week as part of the protracted public sector wage negotiations.

Corrections Minister Elise Archer said Risdon Prison was "under capacity" and the northern prison and $70 million Southern Remand Centre would add capacity.

"There has also been a major recruitment drive for new correctional services officers with a new wave of graduates beginning work in recent weeks to be followed by a further group in coming months," she said.