Australia's three major grocery retailers have admitted stocking seafood from a Thai company accused of using slave labour.

An investigation by the Associated Press has captured evidence of forced labour at a factory outside Bangkok, owned by seafood supplier Thai Union. Some of the workers are children who've said they work under the threat of violence.

Also read: Are slaves catching the fish you eat?

Woolworths, Coles and Aldi have all told Fairfax they use Thai Union as a supplier, and have launched investigations.

"We will investigate this further with our supplier and seek advice from our NGO partners," Woolworths said.

Coles said it stocked frozen prawns that were sourced from Thai Union but said it was proactive on labour issues, working closely with non-government organisations to ensure the products it stocks are ethical.

An Aldi spokeswoman said it would review the reports by the Associated Press after confirming it also sold Thai Union products.

The Associated Press has spoken to workers at the Gig peeling factory outside Bangkok, who have told of working 16 hours a day, under threats of being bashed if they refused to work, or killed if they tried to escape their forced labour.

Their job was to spend 16 hours a day ripping the guts, heads and tails from prawns, or shrimp, for overseas markets, their hands aching from being immersed in cold water. They were paid little, if anything.

The report said many of the workers had been sold to the factory and were migrants from Burma, and those found at the Gig factory included children.

Also read: All supplychains include slave labour

Thai Union president and chief executive Thiraphong Chansiri described the report as a "wake-up call", and said the company would bring all processing in-house to ensure its supply chain does not involve forced labour.

"I am deeply disappointed that despite our best efforts we have discovered this potential instance of illegal labor practice in our supply chain," Thai Union CEO Thiraphong Chansiri said in a statement.

He acknowledged "that illicitly sourced product may have fraudulently entered its supply chain" and confirmed a supplier "was doing business with an unregistered pre-processor in violation of our code of conduct".

Source: AAP