The Chief of Phuket Marine Office 5, Phuripat Theerakulpisut, led police from Patong to make the arrests at the beach, south of Patong, yesterday morning.
About 10 Burmese were held at the scene, where the beach sands have been built up to construct a building that Khun Phuripat reckoned to be 900 square metres.
''The construction was clearly breaking the law,'' said Khun Phuripat, whose authority at sea continues on land up to the high water mark. He is known to have a keen interest in environmental breaches on Phuket.
''I reckon the illegal activity has caused about 9.7 million baht's worth of damage,'' he said.
Officers from Kathu Police Station, which oversees the Patong region on Phuket's holiday west coast, are now looking for the alleged ''owner,'' named as Yutthana Tamchoo.
Other suspicious constructions above the high water mark at Tritrang beach have so far survived claims of official corruption.
The Marine Office 5 telephone number is 076 391174. Khun Phuripat speaks good English.