The Alexander Maconochie Centre is at breaking point, with staff on Sunday forced to cram 340 prisoners into a facility that, until recently, only had 332 beds.

The dramatic increase in inmates has forced the government to consider sending certain inmates interstate, as they push more bunk beds into crowded cells and cottages to expand the AMC's total capacity to 366.

Authorities have built ''physical separation barriers'' in accommodation areas to prevent certain prisoners from mixing, and have stepped up their monitoring of the movements of dangerous detainees.

Ministers will hold urgent round table meetings in coming weeks to find a solution, with a permanent expansion of the jail still only in early design stages.

But Fairfax Media can reveal that a 2001 paper, which was never made public, told the government to expect more prisoners than it is now struggling to house.

The expert report by John Walker Crime Trends Analysis said the ACT, at the very least, would need space for 335 prisoners by 2009, 340 by 2013, and 349 by 2020. The government ignored the report and produced its own modelling, which forecast a much smaller prison population of, at worst, 275 by 2042.

Then corrections minister Simon Corbell later used the lower numbers to back up his government's 2006 decision to reduce the jail's proposed capacity from 374 to 300, in order to keep the project within its $128 million budget.

Within 20 months of opening, the prison was struggling to cope with surging prisoner numbers.

That prompted criticism of Mr Corbell in 2011, with the opposition asking why the AMC's capacity was under so much pressure so soon.

Mr Corbell said the ''most pessimistic'' modelling on prisoner numbers had been used to decide on the jail's capacity, but he did not disclose his government had received the more dire predictions contained in the Walker report.

''Of course those opposite would know … that the government had a detailed projection which it relied upon to make an assessment about the total prisoner capacity … and they would know that the high-end projection, that is, the most pessimistic projection of the requirement in terms of capacity, indicated that by 2040 the total prison population would be expected to be around 275,'' he said in April 2011.

''They know this already, yet they continue to assert that the government made decisions contrary to advice on the issue of capacity at the AMC.''

The prison has held more than 300 prisoners on 99 of the past 280 days. Earlier this year, an inmate with a history of mental-health issues who had previously been marked as a ''prisoner at risk'' killed himself in the jail's health centre. That night, the AMC had 309 detainees, and the 10-bed Crisis Support Unit, designed specifically to care for those suffering mental-health crises, was full.

Corrections Minister Shane Rattenbury said the 40 per cent increase in detainees since January had put pressure on staff, who had responded with professionalism.

Mr Rattenbury, who was not in office during the planning of the AMC, stopped short of criticising the Labor government for ignoring the Walker report. ''The government took decisions on the best advice they had at the time,'' he said.

''Those decisions were taken, we have what we have at the prison, my job now is to make sure we … deal with current pressures.''