PHUKET: The ''unprecedented'' discovery of more than 200 men, women and children of unknown ethnicity in a southern rubber plantation has raised fresh concerns about Thailand's human trafficking industry.

Authorities will tomorrow be seeking to find out more about the families, mostly women and children. They are not Rohingya or Burmese, the two illegal groups most often found in southern Thailand.

With a crackdown underway on the secret jungle camps where Rohingya are held and often abused before being sold to relatives or friends in Malaysia, Immigration officers came across the large, mysterious group about 9pm last night.

Authorities have yet to determine what language the group speaks. They carried no identifying documentation.

Speculation is that they could be from Turkey, Iran or Syria or perhaps even are members of China's Uighur ethnic group.

Unlike the Rohingya, who usually arrive in Thailand with just the clothes they are wearing, the mysterious travellers were dressed for cooler weather than Thailand and carrying backpacks laden with possessions.

Close to where the mysterious group was found, officers also discovered 10 Rohingya men lying in the plantation, too ill to move.

It has become standard procedure for traffickers along Thailand's southern border to discard sick captives if a warning comes that a camp, sometimes containing hundreds of people, is about to be raided.

The Commander of Immigration Division 6, US educated Police Major General Thatchai Pitaneelaboot, led last night's raids to the surprising discovery of the families in the plantation not far from the major city of Had Yai.

On March 4, he took reporters from Phuketwan and the New York Times to Ranong, the port on the border with Burma. The reporters went part of the way out to sea as three longtail boats carried 70 Rohingya men towards Burma.

One of the boat captains later supplied photographs of the Rohingya setting foot back in Burma, not where officials are waiting to greet new arrivals in the port of Victoria Point, but further north, on a secluded stretch of beach.

On March 9, a Rohingya activist encountered five of the men back in Had Yai, southern Thailand. Five other men had been sold onto fishing boats, they told the man, while most of the rest were in the Thai-Malaysia border town of Pedang Besar.

If Rohingya deported back to Burma quickly reappear in southern Thailand and mysterious ethnic groups are now appearing, just how lucrative is human trafficking now? The industry appears largely untroubled by arrests at sea or on land.