Tasmania's auditor-general is blaming a 30-per-cent surge in prisoners over the past five years on the Government's family violence and mandatory sentencing agenda, leaving an understaffed Tasmanian Prison Service (TPS) unable to operate efficiently.

Key points: A report reveals a 30-per-cent increase in inmate numbers over five years

A report reveals a 30-per-cent increase in inmate numbers over five years The Tasmanian Prison Service has not operated within its allocated budget for five years, requiring millions of dollars in additional funding

The Tasmanian Prison Service has not operated within its allocated budget for five years, requiring millions of dollars in additional funding The number of hours prisoners spend in lockdown has increased by more than 2,000 per cent

Auditor-general Rod Whitehead handed down his report into the prison service on Tuesday, raising concerns over officers' increased sick leave and workers compensation that he said was "indicative of an unhealthy workplace".

According to the report, average annual inmate numbers rose from 472 to 613 between 2013-14 and 2017-18, an increase of 30 per cent.

Inmate numbers were at 692 at the end of June this year.

The report said the increase was due to the Government's reform agenda on family violence and mandatory sentencing, an unprecedented increase in those on remand, and a backlog in the Magistrates Court.

The report comes as Tasmania's Parliament prepares to debate a new government bill next week to introduce mandatory sentences for sexual offences against children and assaults on frontline workers.

The report said the Justice Department did not recognise that the increase in prisoner numbers was sustained — rather than an anomaly — until 2016-17.

"In short, [the Tasmanian Prison Service (TPS)] did not have enough correctional officers to effectively and efficiently run the prison service," the report said. "Inmate numbers have now reached levels not previously experienced by TPS."

More prisoners are being placed in lockdown at Risdon prison. ( ABC News: David Fraser )

Union and lawyers find audit 'appalling', 'horrific'

Public Sector Union boss Tom Lynch said the Justice Department should have been able to predict the increase in inmate numbers.

"We have been telling the community for the last two years that we have a prison system that is overloaded with inmates and under-resourced with staff," he said.

"I think it's appalling that we were unable to predict exactly what everybody knew would happen when you cut bail, and you reduce other options."

The report found the TPS had not operated within its allocated budget for the past five years, requiring an additional injection of millions of dollars each year.

At the same time, the number of hours inmates spent in lockdown rose by more than 2,000 percent, from 14,349 to 344,617, due to not enough staff being rostered to run the prison service effectively.

Prisoner's Legal Service representative Jonathon Budgeon said conditions for inmates were "horrific".

"There is total overpopulation, there are a lack of rehabilitation resources, and the tough-on-crime stance from this Government simply just doesn't work," he said.

Mr Budgeon said sometimes lockdowns meant prisoners could not access medications, legal representatives and rehabilitation courses.

"You can't expect prisoners to be civil in those sorts of situations, when their human rights are being severely breached by this Government," he said.

The report revealed the number of employees taking sick leave for more than 10 days increased from 26 percent in 2013-14 to 40 percent in 2017-18, with levels for correctional officers even higher, going from 28 per cent to 46 per cent.

The Prisoners' Legal Service says conditions are horrific. ( ABC News )

Workers compensation claims increased by almost 60 per cent.

"The substantial growth in sick leave and workers compensation leave evident over the last five years is concerning," the report said. "In part, it reflects the challenging nature of employee roles within the TPS, but it is also indicative of an unhealthy workplace, representing a systemic problem within TPS. "It also indicates TPS's related management strategies have not yet been effective in overcoming these impacts."

Mr Whitehead said the prison service had not employed enough correctional officers, meaning it relied on overtime to fill rostering vacancies.

He said increased overtime led to an increase in sick leave, which then contributed to even more overtime becoming necessary in a "downward spiral".

Corrections Minister Elise Archer said the Government was recruiting an additional 90 correctional officers by the end of next year.

She said the TPS was implementing the auditor-general's recommendation of a full review of the service's roster, increasing resources available to the workers compensation management team, and developing an agency-wide strategy to focus on recruitment, leadership and management capability.