Thai fishing fleets have shifted to remote and ecologically vulnerable waters off the east African coast to evade a regional crackdown on illegal fishing and human trafficking, environmental watchdog Greenpeace said Thursday.

Thailand is the world's fourth-largest seafood exporter but its multi-billion dollar industry is largely unregulated and rife with rights abuses.

"Without a a much-needed monitoring system in such distant high seas, there is no control over what happens there," said Anchalee Pipattanawattanakul, from Greenpeace Southeast Asia.

The kingdom came under heavy international pressure to clean up the scandal-hit sector after the European Union threatened to ban all Thai seafood products last year.

But despite government efforts to rein in illegal practises and clamp down on human traffickers, violations remain rampant onboard vessels that have moved to faraway and poorly policed waters, according to a new report by Greenpeace.

According to the watchdog, up to 76 Thai-flagged vessels shifted their operations to the Saya de Malha Bank, an area off the coast of Africa, after crackdowns last year in Indonesia and Papua New Guinea -- common fishing grounds for Thai ships that long ago depleted stocks off their own coastline.

The bio-diverse and environmentally fragile bank, which lies more than 7,000km away from Thailand, has become a "haven for rogue Thai fishing operations over the last 18 months", the report said.

Many of the ships transport their catches back to Thailand through refrigerated reefer vessels, allowing captains to keep their crews at sea -- and out of the purview of authorities -- for extended periods of time.

This practise, known as transshipment, has given unscrupulous fishing operators a free hand to continue to exploit their labour and degrade the environment, the watchdog said.

"These Thai fleets remain as ruthless as ever," Pipattanawattanakul said, calling on Thailand to consider banning transshipment altogether.

Thailand's fishing department, which did not respond to requests for comment, has won some cautious plaudits over the past year for rolling out new regulations and moving to register ships and workers.

The US upgraded Thailand in its annual human trafficking report in July, citing significant efforts to eliminate forced labour in the seafood industry.

But it stressed that corruption continues to undermine reforms and that trafficking and other labour abuses in the fishing sector remain a "significant concern".