A Kiwi could face the death penalty after being charged in a Bangkok meth bust.

New Zealander Isidor Rein, 62, was detained on Sunday in Thailand after he allegedly received a briefcase with a secret compartment containing 2.060kg of crystal methamphetamine from a Nigerian man and Thai woman to take to New Zealand.

The Ministry of Foreign Affairs says it is assisting a New Zealand citizen in Thailand.

"The New Zealand Embassy in Bangkok is in contact with local authorities regarding the arrest of a New Zealand citizen in Thailand," a ministry spokesman said.

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He said for privacy reasons, however, the ministry was unable to provide further details.

A top international aid lawyer says Kiwis detained in jails overseas faced "immense stress and uncertainty" with potentially disastrous outcome.

Founder and director of LawAid International Chambers Craig Tuck said that as more Kiwis travel overseas, the number that are running into trouble with the law was also growing.

Tuck specialises in human rights cases and transnational criminal law and his group has represented clients or advised on cases across 15 countries including Thailand, Indonesia, China, Australia, Fiji, Malaysia, Peru, Mexico, the United States and the UK.

It is feared that Rein could face the death penalty in Thailand, which is one of 58 countries that still retains capital punishment.

The law in Thailand allows the imposition of a death sentence for 35 crimes, including drug trafficking - but rarely imposes it.

Tuck said Kiwis detained overseas faced difficulties including language and cultural barriers as well as rule of law issues.

"The net result is that people feel alone, without voice or understanding of their predicament, detained in cramped dirty conditions with many others and subject to physical force."

On top of that, there could be intense media interest from freelancers who have the sole task of staking out places such as police stations for photos and commentary, Tuck said.

He said it was critical that this was also managed by an appropriate representative.

"It is said that many cases are won or lost at the police station – from our perspective this is true," Tuck said.

The process and penalties could be harsh and needed to be carefully navigated, he said.

"The death penalty is imposed in the many thousands each year – with the sentence being carried out regularly and often in barbaric fashion with hangings, beheading and firing squads."

Since 1935, Thailand has executed 326 people - the latest being June 18, 2018. More than 510 there remain on death row.

Tuck's career has required jail visits across the globe – some of the conditions were simply "unimaginable" for those who accept that "humane containment is part of a civil society".

"In many countries the jails are akin to zoos," Tuck said.

His group regularly used private investigators, cyber security experts, psychiatrists and psychologists to help people who had been detained overseas.

Political and diplomatic intervention was always tricky, Tuck said.

"Governments and diplomats have an obligation to maintain a relationship above and beyond the person detained," he said.

That is why specialist advocates were so important to tackle some of the issues, he said.

This sentiment was echoed by a LawAid International Chambers colleague, barrister Thomas Harré.

"One point to note is that Kiwis detained overseas cannot expect substantial assistance from the NZ Government," Harré said.

"The consulate will be able to assist with a list of lawyers that the person can contact, inform that person's next of kin, help arrange the transfer of funds, and attend court hearings as observers."

Harré said they had worked across a broad range of jurisdictions, particularly within Southeast Asia.

The cases often involved drugs charges, or situations which might point to human trafficking, he said.

The "romance scam" was a classic example in which a vulnerable person was tricked into carrying drugs for an organised criminal group, he said.

"The deception involved there turns the situation into a highly exploitative one."