An American man and his Thai wife, accused of illegally building a floating home - called a seastead - close to Thai territorial waters in the Andaman Sea, are believed to be hiding on Tarutao Island to escape police arrest.

A seastead is a permanent settlement on a structure located at sea outside the jurisdiction of any country.

Officers in Phuket are forming a team to hunt the couple after seizing their house, viewed as a threat to Thai sovereignty and the environment, and taking it ashore late on Monday night.

The 46-year-old American bitcoin investor Chad Andrew Elwartowski and his wife Supranee "Nadia" Thepdet were not in their seastead during an inspection on April 12. The latest clue indicated both were in Tarutao, police said, but believed they already turned off their smartphones to prevent investigators locating them.

The investigators earlier found the couple had allegedly persuaded people to build seasteads off the coast of Phuket. They claimed the area is in international waters, so it can be declared a so-called independent state.

The couple's floating house -- a six metre-wide platform installed by Ocean Builders -- was located about 14 nautical miles (26 kilometres) off the Phuket shoreline.