The parents of a young autistic man shackled to a hospital bed for 14 days have accused authorities of abandoning their son and pleaded with them to end their "nightmare" and allow him to return home.

James Pascoe, diagnosed with Autism Spectrum Disorder when he was two years old, spent his 21st birthday chained to a bed after he was taken to The Northern Hospital, Victoria in Australia on 21 November.

Parents Bronwyn and Allan Pascoe claim they repeatedly asked the Australian Department for Human Services for help treating James, who as a result of his autism can lash out when scared or anxious, but were ignored.

A Change.org petition in which they call started by the couple last week, soon after they discovered James’ treatment, has already gathered nearly 40,000 signatures.

He remains tied to his bed today, with Australia’s Herald Sun reporting a sixth constraint, across his stomach, had been added. It is one short of the legal limit.

His mother, who was a nurse, also claimed that he had been given heavy doses of drugs to sedate him.

“It sounds unbelievable. But it's the nightmare we've been living. The last 11 days we've had little sleep,” Mrs Pascoe wrote on the petition.

In November, James was moved to a supported accommodation centre in Whittlesea where he lashed out causing staff to ring the police who took him to hospital on the 21. Later the same day he panicked again and was hospitalised.

Writing on the petition Mrs Pascoe added: “It's heart breaking to think just 2 years ago he was happily walking around SeaWorld with his grandmother and Aunty.

“Now thanks to mistreatment he's anxious and lashes out in fear and anxiety and lack of coping due to his unresolved grief and loss.”

James’ behavioural therapist Jeanette Coombes told the Herald Sun: “In my professional perspective the longer he is in this environment the higher his trauma response will be”.

“He is doing what he can to communicate his distress. He is scared and (anxious) and wants to be around people he knows — he just wants out,” she said.

Mrs Pascoe’s mother used to care for James – calming him down and providing a stabilising influence – but after her death from pancreatic cancer in 2012 James behaviour changed.

“He withdrew and became depressed and became obsessed with the fact that people died,” Mrs Pascoe told Daily Mail Australia.

A spokesperson for the Department of Human Service told the Daily Mail Australia: “James was admitted to the Northern Hospital by his family. His family and a consulting physician are making decisions about his care while in hospital.”

“While several options for support have been offered for James’ long term care, these options have not so far been accepted by his family.”

The statement continued: “The department will continue to work with James and his family to make sure he gets appropriate and quality care.”