A high-profile New Zealand lawyer has warned the family of a Kiwi man detained in a Bali jail to be "really careful".

Tauranga-based human-rights lawyer Craig Tuck has been counsel for several New Zealanders caught up in legal proceedings in Indonesia, including drug trafficker Antony de Malmanche.

Tuck became aware of the most recent plight after reading the Herald's article on a New Zealand citizen who lives in Western Australia who was has been arrested in Bali.

Matthew Arai, also known as Matty Isiah, has been locked up in a "urine and flea infested" Bali jail after reportedly being arrested for attempted murder outside a popular nightclub.

Arai was in Kuta with his wife and son for a cousin's wedding when the incident occurred.

He was leaving the nightclub early on Sunday morning and struck a scooter driver while attempting to flag down a taxi, according to an Australian media report.

Ngaarda Media said the New Zealander claimed the incident was an accident but he was arrested and thrown in jail.

A co-worker of Arai's, Regan Jhonson, said the incident was a misunderstanding.

"He came out of a nightclub to flag a taxi, he's put his arm out and a scooter has ridden up along the footpath and driven straight into his arm and straight away he was mobbed by locals because they thought he had hit the rider and then he was arrested. He's been arrested for attempted murder."

Bali police have also allegedly demanded payment of almost $10,000 (US$7000), or Arai would have to stay in jail.

Tuck told the Herald that Arai and his family needed to take extreme caution in that environment.

"It is all fun and games for people visiting but when it goes wrong, it goes horribly wrong," he said.

"If he has been detained and is going to be charged, then it is a very serious situation because he will be transferred to Bali Polda.

"He will then require a local lawyer and a number of police lawyers will approach him," he said.

"He wouldn't want to be locked up and then proceeding on an attempted murder charge because you can get one year in jail for a small amount of cannabis. That would be very stressful for him."

Tuck said it appeared from photos that Arai was currently being held at a police station.

"He obviously hasn't been taken to Bali Polda, which is the main detention centre in Denpasar run by the police. It is where most people get detained initially," he said.

"This is a very crowded, intense environment, where people are essentially sleeping on the floor, they are being brought food and water by people that are supporting them – friends and family.

"It is intensely hot and a very stressful environment. From my experience over there, generally there are a number of people - up to 20 - in a small, confined space."

Beyond the prison cell, Tuck said the Indonesian legal system is quite different to the New Zealand and Australian judicial processes.

"You have to be really careful commenting on the police and judicial system over there.

"There is a police force that many are paid to get a job essentially, and there are numerous instances of police corruption," he said.

"There is a lot of arbitrary decision-making around who gets charged, what the cost of that is, and how it can be resolved.

"The locals are fearful of any engagement with the police and certainly in our dealings with the police stations and jails over there, many are concerned to even get close to those areas."

Tuck said Arai's family should err on the side of caution when it comes to paying any monetary demands.

"Where is that money going would be the first question, and what does it achieve," he said.

"There are real difficulties with this because what happens over there is, once you start paying people off, it actually ramps up the game a lot more than you think.

"The next level of decision-making will say 'well you paid the street cops or whoever $10,000, we are the next level up so we need more than that' - and that can work all the way through the court system."

Tuck said he had not had any contact with Arai's family but would be happy to offer his services if needed.

"We have lawyers over there that we trust and that we use, so we would be more than happy to assist if that is what they want."

Yesterday, Arai's mother, Wendy Clark, told Ngaarda Media she was very upset and looking for a lawyer who could help the family.

"It is very distressing to see my son in a one-metre cell on the floor. There's urine and it's flea infested.

"He's not allowed a seat, he hasn't got a bed and I am not leaving Bali until I get my baby out of there," Clark said.

The Ministry of Foreign Affairs and Trade confirmed the New Zealand embassy in Jakarta was providing consular assistance.