They roamed the seas off the Andaman Coast for generations, but Thailand's sea gypsies say their traditional way of life is under threat and their homes at risk from a tourism boom.

The plight of the once-nomadic hunter-gatherers highlights the growing pressures on marginalised indigenous people in a country seeing a surge in foreign visitors to a record 22 million people last year.

The creation of protected marine parks, the depletion of fish stocks and a construction frenzy are all making it increasingly hard for the kingdom's "Chao Lay" sea people to maintain their age-old lifestyles.

Although they often spent time away at sea, Nang Miden says his ancestors have lived on the island of Phuket since long before it was transformed from a sleepy tropical backwater into one of the kingdom's top tourist destinations.

Nowadays prime beachfront on the crowded island is scarce, and Nang is threatened with eviction by a property developer who bought the land from under his feet and wants to move him to a new site further inland.

"I have lived here since this area was jungle," the 78-year-old told AFP, sitting outside his simple home in the Rawai village of roughly 2,000 sea gypsies, where he sells fruit and shredded coconut.

"My ancestors lived here before me. I have nowhere else to go. We have lived here for hundreds of years already."

Many older Chao Lay cannot read or write and were unaware they could register land as their own. Ownership is also an alien culture to them, so many lack land title deeds.

In Nang's case, a local businessman obtained title deeds for the land several decades ago. When he failed to keep up the payments on a bank loan, the plot was seized and sold on to the current owner.

In a major blow to the community, a Phuket court in February ordered seven households to vacate their homes. They plan to appeal, and face a long legal battle.

In the meantime, their lack of official ownership means many villagers live in slum-like conditions, denied access to running water and electricity.

In the past the sea gypsies led a nomadic existence, trading fish, sea cucumbers and other bounties of the ocean for the little they needed.

In recent decades they have become more sedentary, and face the threat of arrest and seizure of their boats if they hunt in national parks. Scuba divers sometimes sabotage their fish traps to protect marine life.

"After the Phuket boom, our places to work have been fewer and more limited. Whatever we do is wrong. Fellow villagers are often arrested," said Nirun Hyangpan, a 37-year-old representative of the Rawai sea gypsies.

Experts say that despite their increasing exposure to the modern world, the Chao Lay's affinity with the sea remains as strong as ever.

Some cannot sleep unless they hear the sound of the waves, and they struggle to find jobs on dry land so remain heavily reliant on fishing.

"These people need a beachfront area where they can moor their boat and forage. It's not only spiritual - it's their way of life," said Narumon Arunotai, an anthropologist at Chulalongkorn University in Bangkok.

"Traditional fishing is impossible these days because the sea is almost depleted so if you use fish spears or small fish traps then you won't be able to get any fish," she said.

"But they still feel that they're children of the sea."

There is a glimmer of hope for the Rawai community, as the government is analysing old aerial photographs and other evidence such as bone discoveries to establish if they arrived before the property developer.

"If it's true they lived there longer, they should have more rights to the ownership deeds," said Prawut Wongseenin, head of the bureau of consumer protection and environmental crime at the Department of Special Investigation.

"To win their appeal, they need scientific evidence," he said.

There are an estimated 12,000 Chao Lay in Thailand, comprising three different ethnic groups - the Moken, the Moklen and the Urak Lawoi.

Their plight gained attention after a massive tsunami in the Indian Ocean in 2004 put the spotlight on afflicted coastal communities.

The Moken attracted international interest for reading the signs of the impending tsunami, fleeing to higher ground before the killer wave struck.

They are also skilled free-divers and, unlike other humans, can focus underwater without masks These days, however, even their time underwater can be dangerous.

Unscrupulous businessmen sometimes pay them to go dynamite fishing, while the air compressors and hoses they use to spend longer on the seabed leave them at risk of permanent injury or even death from decompression sickness.

Some also lack citizenship, which hinders their access to healthcare and other public services.

In 2010, the Thai cabinet passed a resolution setting out a policy to protect their way of life, but the sea gypsies say that in reality it has made little difference.

While there is no official policy to assimilate the Chao Lay into mainstream Thai culture, at school they are taught the Thai language and history, not about their own roots or Austronesian language.

"Institutions act to socialise these people to become Thai and to forget - and in many cases become ashamed - of who they really are," said Narumon, the anthropologist.

With Thailand welcoming ever more tourists - almost nine million in the first quarter of 2013 alone - the Chao Lay fear for their future.

"If tourism keeps on booming with more beachside hotels, spas and resorts, the sea gypsies' way of live will continue to disappear," Nirun said.

"It's like killing us alive."