Swiss food giant Nestle vowed Tuesday to stamp out any forced labour used in its supply chain in Thailand, after a probe confirmed workers were toiling in slave-like conditions to catch and process fish for Nestle products.

"Nestle is committed to eliminating forced labour in our seafood supply chain in Thailand," executive vice president of operations Magdi Batato said in a statement sent to AFP.

Nestle had commissioned non-governmental organisation Verite to investigate working conditions among its suppliers of fish in Thailand following allegations they were using slave labour.

The Verite report concluded that forced labour and other human rights abuses were "endemic" and posed an "urgent challenge to any company sourcing seafood" in Thailand.

In some cases, impoverished illegal migrants trafficked from places like Myanmar and Cambodia were tricked and "sold" to fishing vessels where they worked virtually non-stop in dire conditions, receiving little or no pay.

The workers questioned for the investigation, conducted over three months at six production sites, testified to "horrible and dangerous" conditions, describing physical violence, intimidation and threats.

Workers were sometimes forced to sleep on the floor when they were allowed to rest, and had limited access to water, medicine and sometimes food, the report found.

Their passports or ID cards were often taken to ensure they would not leave before their contract ends, and their wages were often withheld for months while they were at sea.

This sometimes resulted in them or their families taking high-interest loans from the employer, and landing them in debt bondage, the report said.

Verite faulted the lack of transparency in the supply chain, with boat workers often isolated at sea for months at a time at the mercy of their captain and no possibility to communicate with the outside world.

The NGO urged Nestle and other companies to strengthen "supply chain mapping and traceability efforts, making current monitoring and capacity building initiatives more robust."

Nestle commissioned the Verite report after pet food buyers in the United States filed a class action lawsuit in California claiming they would not have purchased Nestle's Fancy Feast products had they known they had ties to slave labour.

The Swiss food giant countered at the time that it required "all of our suppliers to respect human rights and to comply with all applicable labour laws."

However, it said it would ask Verite to investigate, acknowledging that enforcing its strict code of conduct throughout the complex, multi-layered supply-chain in the Thai seafood industry that supplies some ingredients for its products was a challenge.

After seeing Verite's conclusions, Nestle said it had launched a 10-point action plan, including setting up an emergency response team to quickly help individuals at risk.

The plan, which Nestle said it would begin implementing immediately, also includes a programme aimed at verifying the working conditions on fishing vessels, a programme to train boat captains in best practices and a system aimed at improving the traceability of seafood ingredients used in the company's products.