A Thai court found dozens of people guilty of human trafficking offences on Wednesday in a mass trial exploring links between corrupt officials, including a senior army general, and the grim but lucrative trade in Rohingya and Bangladeshi migrants.

Thailand's junta launched a crackdown in May 2015 on a network funnelling desperate migrants through southern Thailand and onto Malaysia, holding some for ransom in jungle camps.

It unspooled a crisis across Southeast Asia as gangmasters abandoned their human cargo in the camps where hundreds died from starvation and malaria, and at sea in overcrowded boats which were then "ping ponged" between Thai, Malaysian and Indonesian waters.

Rights groups long accused officials of ignoring -- and even orchestrating -- the trade in humans through Thailand's southern provinces.

The area was the crucial link in a criminal trail that stretched from Myanmar to Malaysia.

The crackdown revealed a lattice of military, police, local political and mafia figures acting as traffickers, agents and logistics men, all soaking up cash from some of Asia's poorest and most vulnerable migrants.

On Wednesday judges at Bangkok Criminal Court began delivering a stream of verdicts for the 102 defendants. One other accused died while on remand.

The offences include human trafficking, ransom and murder. All deny the charges.

Media were barred from the court itself, relying instead on an audio relay of the complex proceedings.

- Soldiers and kingpins -

Judges placed heavy reporting restrictions on much of the testimony, citing national security concerns. But the case has still lifted the lid on the power networks dominating southern Thailand.

Army Lieutenant-General Manas Kongpan, a top figure in the security apparatus covering the south, is the highest-ranking official on trial.

In 2013 he was promoted to head the Internal Security Command (ISOC) for the south. Current junta leader Prayut Chan-O-Cha was army chief at the time.

Another well-connected alleged kingpin is Pajjuban Aungkachotephan, better known as Ko Tong or 'Big Brother Tong'.

Police accused him of using private Andaman Sea islands, close to tourist spots such as Koh Lipe, to shift boatloads of migrants to the mainland, where they were packed into lorries and taken to the fetid camps straddling the Malaysia border.

An army captain, four ranking police officers, a nurse and several officials, including the mayor of Pedang Besar in Satun province, are also among the accused.

By the lunch break a drip feed of 38 defendants had been convicted for a range of offences including human trafficking and slavery.

Among them were guards at the jungle camps where migrants were held, including a Rohingya man who acted as an interpreter, and a string of local officials.

Thailand's role as a key trafficking route spilled into full view after officials found dozens of shallow graves in the hidden camps dotting the steep, forested hills of the Thai-Malaysian border in May 2015.

They revealed the horrors endured by some of migrants, who were starved and held in bamboo pens by traffickers who demanded up to $1,000 for their release.

- 'Big business, big money' -

The verdict is being closely-watched inside and outside Thailand.

The government is desperate to dispel the kingdom's notorious reputation for human trafficking and close one of the darkest chapters in the country's recent history.

Junta chief Prayut angrily denied the case reflected systemic corruption within the security services.

"Manas alone will not make the entire military collapse," he told reporters.

Critics say the case was prematurely concluded and describe a trial marred by witness intimidation, secret evidence hearings and restrictions on media reporting.

"We expect there are many more perpetrators out there," Amy Smith, from Fortify Rights, told AFP.

"This is a big business with big money."

The senior policeman who initially headed the investigation, Major General Paween Pongsirin, fled Thailand under threats to his life.

Days before he left he told AFP the case had been pulled before it could delve further into the complicity of officials.

Stateless Rohingya Muslims have fled neighbouring Myanmar in their tens of thousands since sectarian violence flared in 2012.

They were joined by Bangladeshi economic migrants on a rickety boats southwards across the Andaman Sea, seeking work and sanctuary in Malaysia and Indonesia.

Thousands are believed to have died at sea, in a migrant flow that garnered few headlines until the trafficking crackdown in 2015.

Source: AFP