Queensland's jails have reached capacity, with the number of prisoners exceeding the number of built beds.

Data from monthly Corrective Service Department reports shows there are 6,836 prisoners in custody while there is a built bed cell capacity of 6,827.

It shows inmate numbers have been rising by more than 100 per month for the past few months.

Opposition police spokesman Bill Byrne says State Government policies are to blame.

"[In] shortly over 12 months, [there has been] a massive increase in the prison population in this state," he said.

"We know overcrowding is occurring in many of the facilities.

"We know there have been disturbances in some of those facilities.

"We also know, and I know from personal experience, many prison officers, corrections officers, are increasingly concerned about their own welfare."

Mr Byrne says it is a result of Government cuts to programs that replaced jail time.

"When you shut those sorts of diversionary programs down, the only effect can be is that you're going to increase the population of prisoners," he said.

"I said that 18 months ago - if you bring these policies in and get rid of these measures all you'll do is fill up the prisons and that's in fact what happened.

"Our estimate is that there's $100 million more being funnelled into prisons simply because of the policy decisions made by this Government."

Mr Byrne says it is "increasingly difficult" to get information from the State Government.

"I find it ironic when the Government talks about open data, that the most simple data that communities need to understand is what's going on for their law and order and their services, how many staff are in the particular roles, the Government's very disinclined to be open and transparent in these matters," he said.

"All I'm calling for in a democracy, is that all the data be provided in an open and transparent way, so normal members of the community with an interest can find out what's going on with their government.

"I think it serves the Government's purpose and misinformation not to make that immediately available."

Union worried about staff safety

The union representing prison workers says Queensland's overcrowded jails are putting staff safety at risk.

Together Union president Vivienne Doogan says it has been an ongoing issue.

"Our members in our prisons have been raising concerns about overcrowding for quite some time," she said.

"The bottom line is - it's an absolute safety issue.

"It has to be addressed and unfortunately this Government's policies of putting lots of people in jail is only going to add to the problem.

"The last 12 months or so, we've had many incidents of more prisoners per room than there needs to be.

"The Government and management have known for some time they're going to get at some point and the reality is, they haven't been addressing it."

Together Union spokesman Alison Bissett-Findley says Maryborough prison in the state's south-east has been over capacity for the past six months.

She says trade courses have also been cut from seven to five days a week to save money and there is a growing sense of frustration.

"What we've got at the moment is a system where the jails are overflowing - the solutions that are being put in place are not real solutions," she said.

"We need to increase the staffing numbers for a start and our members are being put at risk, the community is being put at risk, and the prisoners we've decided to incarcerate because they've done the wrong thing are not being rehabilitated."

Queensland Attorney-General Jarrod Bleijie has been contacted for comment.

However, the department says prisoner numbers are managed on a statewide basis, and fluctuate over time.

It says all prisons can employ a 'surge capacity' strategy, which includes double-up placements in cells and the use of temporary beds.