A witness to the arrest in Bali of a NSW teenager says the schoolboy was picked up in a co-ordinated sting by plain clothes police intelligence officers who had been waiting for hours, apparently tipped off that he had allegedly purchased drugs.



The witness, a shopkeeper at the Mirah mini market, said the boy, 14, was apprehended at about 2pm on Tuesday along with a friend after leaving a foot massage salon across the road on Jalan Padma, a busy street in the heart of the Kuta tourist district.



"It caused quite a commotion. A lot people stopped and watched as they were taken away," said the man, who asked not to be identified, pointing to the pavement in front of the shop.



"I remember the boys looking confused and asked 'why', why were they being taken away."



The shopkeeper said the two youths were arrested by four plain clothes police intelligence officers who had been loitering outside his shop since 11am. There were another two plain clothes officers were down nearer the beach, where the alleged transaction is understood to have taken place.



"They did not search or asked the boys anything, they were just taken away," he said.



The account of the arrest, the first by an eyewitness, strongly indicates that someone who had seen the transaction, or the dealer, had tipped off police.



The witness described the two as "just average looking tourist boys". One of them was shirtless, he added, and each was led away by two officers.



It appears the other boy was let go by police, presumably because he was not allegedly in physical possession of the cannabis.



It is unknown whether the drug dealer was also apprehended by the Indonesian police, who are declining to provide details on the case because the schoolboy is a minor.



The account of the shopkeeper can't be independently verified as a result. But the location and timing of the arrests accords with information already provided by the schoolboy's first lawyer, Sursono.



The witness said the arrest was chaotic. The intelligence officers had initially arrested the wrong people, he said. "I remember they stopped some older tourists before, and they let them go after saying 'wrong guy'."



"Someone tried to video what happened using his mobile phone, one of the intels took the mobile and deleted the video before giving the mobile back".



It is unclear how much cannabis the boy was allegedly caught with, with reports ranging from 6.9 grams to 3.6 grams.



He is being held in a room away from adult prisoners at a Denpasar police station.



He spent a frightening first evening alone at the police station until his parents, with whom he had been holidaying, arrived the next morning.



Lawyer Muhammad Rifan said last night that the boy had been ''crying all day'' and refusing to eat. His parents were depressed and feeling helpless as the enormity of their predicament set in.



''Just like any other parents, they don't know what to do when their child faces this type of situation,'' he said.



Juveniles are typically treated leniently in Indonesia's courts but often get custodial sentences for drug offences. And as there is no juvenile court system, he would be likely to go to an adult prison if convicted.



Indonesian courts can commute sentences for drug crimes to a few months, or even waive jail time completely, but there must be evidence that the accused is a drug addict.



Mr Rifan said if the parents could provide evidence that they had sought treatment for their son in Australia for any addiction, he would probably get off. Otherwise, he could face jail time of six months to four years.



Australian Foreign Minister Kevin Rudd has told Foreign Affairs officials to make the boy a priority.



Mr Rudd said the boy's parents were deeply distressed by their son's incarceration.



''I think if you put yourself in the position of being a mum or a dad with a 14-year-old who's got themselves caught up in this situation, you're heart would go out to the parents,'' Mr Rudd said.



''I have just spoken with our ambassador in Jakarta [Greg Moriarty] and I have indicated to him that his number one priority in the immediate period ahead is how we support this young boy and his family and do everything we can to obtain his early return to Australia.''



The boy is the youngest Australian to be arrested in Indonesia.



''Regrettably, we know the authorities in Denpasar too well through matters we have had to deal with over the years,'' Mr Rudd said.



''I'm not going to be in the business of providing public lectures from abroad on the nature of anyone else's legal regime.



''We respect those laws and we will work very closely with our friends and colleagues in Jakarta and Denpasar.''



The boy could be held at the police lock-up for up to a month while his alleged crime is investigated. If police decide they will proceed with the case, he will be formally charged and face court in Denpasar.



Mr Rifan refused to confirm whether the boy had admitted to buying the drugs.



Drug dealers frequent the throbbing tourist strip around Kuta, often whispering in the ears of passers-by.



It is not uncommon for dealers to then inform police if the buyer is a foreigner, sometimes snaring a lucrative payment for the information.



Bali's only under-age prison is a cell in Kerobokan, an already desperately overcrowded jail that is home to a diverse population of hardened criminals and small-time crooks.



Prisoners mix freely at Kerobokan, where the guards are vastly outnumbered by convicts.



There was a riot at the jail earlier this year, and several inmates are on death row, including Australian Bali nine ringleaders Andrew Chan and Myuran Sukumaran.



Murderers and rapists, including infamous child rapist Mochamad Davis Suharto - also known as Codet or Scar - are doing time there as well.



Cannabis is considered a narcotic in Indonesia on a par with heroin, cocaine and methamphetamine.



Mr Rifan would not confirm the teenager's name and urged media organisations not to publish it, saying it was illegal to do so in Indonesia.



Police also confirmed there would be no ''walk of shame'' in front of cameras for any under-age offenders.