The ACT has fared badly in the latest national figures on imprisonment with an average incarceration rate of 133.8 people per 100,000 adults for the 2015 December quarter up from 125 per 100,000 for the 2015 August quarter and 130 per 100,000 year-on-year.

There were, on average, 89 Aboriginal and Torres Strait Islanders in full-time custody at the Alexander Maconochie Centre over the 2015 December quarter. This was up by 10 per cent from the average of 80 in the 2015 August quarter and 26 per cent year-on-year.

The figures, released by the Australian Bureau of Statistics, logged a spike in the rate at which the ACT jails indigenous offenders which exceeded any other jurisdiction in the country.

As of last Tuesday there were 96 indigenous detainees in custody, 28 on remand and 68 already sentenced.

"I, and ACT Corrective Services, are concerned about the increasing indigenous detainee numbers [but] we do not know categorically what is driving the upward trend," ACT Corrections Minister, Shane Rattenbury, said.

He has asked Justice and Community Safety to investigate what is driving the spike and report back to himself and Attorney General Simon Corbell.

"What seems to have changed? For a long time we went along with our indigenous detainees at about 17 to 19 per cent [of the prison population]," he said.

"That has jumped up into [the] 27 per cent [range] in a period of six to eight months. Is it that the indigenous community is being particularly affected by the meth amphetamine push?"

On average 406 inmates were in custody at the AMC during the 2015 December quarter. About 386 were male. The male incarceration rate of 258 per 100,000 was the second lowest in the nation.

The overall indigenous imprisonment rate was 2,045 per 100,000. The male indigenous imprisonment rate was 3,570 per 100,000. Both figures were below the national rates of 2,324 and 4,263, respectively.

"It [the jump] raises questions about police practice, court practice and how bail is being judged by the courts."

The disappointing result has been slammed by former Labor chief minister and a driving force behind the foundation of the AMC, Jon Stanhope.

Mr Stanhope, an adviser to the Winnunga Nimmityjah Aboriginal Health Service, said Canberrans paid a premium for a world-class "human rights" prison modelled on the best Europe had to offer.

"It has been operating for more than five years now," he said. "AMC should be measured against prisons in Europe that are similarly committed to a human rights culture [not prisons in Australia].

"If it doesn't measure up serious questions have to be asked about what is [the] management doing with the very, very, generous funds they receive. I wouldn't be looking to change the funding; I'd be looking to change the management."

The ACT spends about $150,000 per inmate per annum, well above the national average of $110,000 per inmate per annum and more than three times the American spend of $45,000 per inmate per annum on AMC detainees.

Mr Rattenbury rejected the suggestion ACT Corrective Services had lost its way, telling Fairfax Media the commitment to a "human rights" prison was as strong as ever and he had "the utmost confidence" in the ACT Corrective Services management team.

Professor Lorana Bartels, an associate professor in the school of law and justice at the University of Canberra and an advocate for sentencing and prison reform, said the ACT was starting to look like the rest of Australia in terms of the rise in imprisonment rates.

"I can't entirely understand the trends because they have been in the absence of punitive policies," she said.

"The government has taken steps to try and address the rise [in rates of incarceration] but they just don't seem to be working."

Historically, prior to the opening of the AMC when ACT prisoners were incarcerated in NSW jails, imprisonment rates have been both higher and lower than they are now.

In 1984, the first year accurate imprisonment statistics for the Territory were produced, the average imprisonment rate was 60 people per 100,000 adults. This had blown out to 199 per 100,000 in 1999 but was down to 110, then the lowest rate in Australia, by March 2014.