He said soldiers came to his workplace on Friday and talked to the Thai manager, who then told the employees all Cambodians working illegally must return home by order of the military.

"When I first heard this from the owner, I felt OK, I didn't feel scared or afraid," the 20-year-old said. "But when I saw the soldiers approach me, I felt scared. I decided then to go with them straight away, without complaint."

He said the soldiers did not mistreat him, and took him to a railway station, from where he was transported to the border.

Roads leading to the Cambodian border were packed on Sunday with trucks and buses full of Cambodian workers opting to head home rather than face any possible confrontation with the Thai authorities.

"The NCPO has no policy to sweep and clean, but teams must go to areas where there are illegal labourers to organise and manage the foreign workforce, as we have accumulated problems over the past 10 years," said NCPO spokesman Winthai Suvaree. "We ask that those who employ foreign workers continue their activities as normal and maintain good order."

Cambodia's Foreign Ministry said it would ask Thailand to ensure better treatment for those leaving. "We request that they send workers in a humanitarian way, or without prosecuting, and facilitate the legalisation of undocumented workers," said ministry spokesman Kuy Kuong.

Chem Cheda said he plans to apply to return to work legally.

Rights groups said they were unaware of departures by the larger community of migrant workers from Myanmar.

The junta estimates there were 90,000 people living illegally in Thailand. The exodus could prove disastrous for the Thai economy, which relies heavily on foreign workers to perform jobs Thais are reluctant to do, including manual labour and domestic work.