A witness to the attack, which happened at about 9.30pm on Saturday night, said it was “unprovoked” and had happened at the Bali resort where the young man was staying.

“They had him tied at the legs with a garden hose and he was handcuffed and broke two sets of handcuffs,” according to the witness, who did not want to be named.

“He was having psychotic episodes every couple of minutes. He was unable to lie still and you could not understand much of what he was yelling. I do not believe it was a language. He was yelling throughout 'get out of me'. It was like he was possessed – the only way I can describe it.

“The noises he was making was like a wild animal and extremely loud that could be heard whilst inside my room with the television blaring to try to drown out the noise.

“As a mother I was extremely concerned for this young man and believe he required treatment earlier. Another lady at the resort phoned his parents in Darwin and asked them to contact the Australian Consulate (yes we live in a wonderful country) and once they did within minutes he was receiving medical treatment.

“I couldn't understand why medical treatment couldn't be given before this, but apparently [it was] because the young lady's consulate was involved they wanted him arrested first.

“The police were scared of his behaviour, and when they moved him from the concrete just outside the resort to the grassed area inside it took many, many men to carry him.”

The young woman, a Czech tourist, is believed to still be in hospital being treated for facial injuries.

The Australian man has returned to his home in the Northern Territory after recovering from the effects of the “magic mushrooms”, which are openly available in the Bali's nightclub district.

The witness, who was in Bali accompanying her own son and his mates at schoolies, said she hoped every schoolie read about this incident and took notice.

“But unfortunately they are 10 foot tall and bulletproof and believe that this would never happen to them,” she said.

Bali police said the man's parents had immediately flown from Australia when they heard of the incident and had “settled” the matter with the woman's family. As a result, she would not press charges, they said.

Police chief I Gede Putu Dedy Ujiana said they did not arrest the boy because he was clearly suffering from the effects of the drug. He was taken instead to the Bali International Medical Clinic, where he continued to make trouble, allegedly breaking restraints on his bed.

Australian consular officials confirmed they had offered consular support to an 18-year-old man earlier this week, but would not provide further details.

Paul Mergard, the Bali co-ordinator of community group Red Frogs, which helps schoolies, said magic mushrooms were one of the worst threats for revellers in Bali.

In the week his group was there, they had sent perhaps 10 young people to hospital suffering “quite significant effects”.

“There was lots of anxiety ... they were hallucinating and seeing weird things. Some reported that their vision had gone funny and they were seeing things that were not there,” Mr Mergard said.

Bali police say that, while psilocybin, the drug contained in magic mushrooms, is illegal in Indonesia on its own, the mushrooms themselves are not. As a result they are openly spruiked and advertised in the Kuta area.