A social worker says up to six children are being kept in solitary confinement in a maximum-security adult prison in Victoria.

Last month, revelations a 16-year-old Indigenous boy spent several months in solitary confinement at Port Phillip Prison sparked calls for an urgent investigation.

Youth worker Chantelle Higgs visits the Charlotte maximum security unit inside the prison, and has told 7.30 Victoria that case is not an isolated one.

She says there are currently five or six other children being held in solitary.

"I've known of at least one teenager to spend between six-and-a-half and seven months in Charlotte, which is almost unfathomable to think about what that would do to somebody," she told 7.30 Victoria.

"I would say it's damaged him beyond words to describe the effect it's had on him ... he's not really recovered."

She says the Charlotte unit is a "stark environment".

"There's no natural light, no natural air. Often there is either dead silence or the sounds of really unwell people in the background," she said.

"One young man told me once a banging sound had gone on for 24 hours - another prisoner had been banging on the walls for 24 hours."

She says within the solitary unit, people are locked down for a minimum of 22 hours.

"They don't have access to any rehabilitation, they don't get to go to school, they don't get to learn, they don't get access to mental health practitioners," she said.

"It's a really depressing environment and a lot of people will leave with mental health problems if they don't already have them.

"It breaks people."

She says the youth have nobody to advocate on their behalf.

"The parole board has made these decisions behind closed doors," she said.

"It's hard to imagine that a magistrate in a children's court would sentence a child to solitary confinement."

Andrew McIntosh, a spokesman for the Victorian Minister for Corrections, says the report is wrong.

In a statement, he said the State Government is restricted from commenting on individual cases.