The Ashley Youth Detention Centre was on Monday housing 26 children - a number not seen in at least a decade, according to the state Children's Commissioner Leanne McLean.
The centre was described as posing a "current" abuse risk in the final report of an inquiry into child sexual abuse in state institutions, published in September.
The state government, which in 2021 promised to shut the centre in 2024, has shifted to a mid-2026 closure timetable as part of reshaped justice reforms.
The union which represents Ashley workers says the detainee-to-staff ratio is dangerous. (Ethan James/AAP PHOTOS)
Ms McLean said the number of detainees at the centre was the most since her appointment to the role in 2018.
"This (is) despite the commission of inquiry's recommendation, accepted by the government, that this institution is not fit-for-purpose (and) must be closed," she said.
Ms McLean said almost all the children were being held on remand, awaiting legal proceedings.
"Conditions at Ashley remain extremely concerning, with low numbers of staff attempting to meet the highly complex needs of children and young people," she said.
Ms McLean said isolation practices were regularly being used to manage safety as a result of low staff numbers.
Robbie Moore, the state secretary of union HACSU which represents Ashley workers, said the detainee-to-staff ratio was dangerous.
He said under current staffing models, the maximum safe number of detainees was about 15.
"The infrastructure at the site is very old. It is not a suitable ongoing environment (and) it doesn't reflect contemporary practice," he said.
"(Staff) morale is extremely low.
"These people want to support children (but they are) without adequate staffing to provide the therapeutic support."
Ms McLean has called for a task force to reduce the number of children at the centre, something Premier Jeremy Rockliff said was being "scoped".
She said therapeutic home-like residential care facilities were urgently needed, in advance of government plans for new bail accommodation and other facilities.
Jeremy Rockliff says his government remains committed to closing the centre. (Rob Blakers/AAP PHOTOS)
The Tasmanian government is working to implement 191 recommendations of the inquiry and is set to provide a progress update on Thursday.
"We will always be tough on crime and tough on the causes of crime. We can do both," Mr Rockliff told state parliament.
"I reiterate my very clear intention to close Ashley as soon as possible."
TasCOSS, the peak body for community services in the state, said groups were ready to work with the government to transition children to community-based care.
"TasCOSS shares the serious concerns of the commissioner and echoes her call for ... an urgent task force," CEO Adrienne Picone said.
The inquiry heard harrowing stories of sexual and physical abuse at the centre across decades.
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