A 'paradise-like' Thai island famed for its white beaches and turquoise blue sea is to close indefinitely after authorities said it had been ruined by tourists. Koh Tachai, off the west coast's Phang Nga province, will be off-limits to all visitors for an indefinite period from 15 October 2016.

The closure comes on the back of heavy tourism damaging the island's environment and natural resources, the Bangkok Post has reported. The island is part of Similan National Park, a natural conservation area that is supposed to be heavily protected.

The park's archipelago of 11 islands – famous for its dive sites – are closed every year during the monsoon season from May until October. Koh Tachai will remain closed beyond October, however, as attempts are made to allow it to recover from overuse.

Assistant professor Thon Thamrongnawasawat, deputy dean of the Faculty of Fisheries of Kasetsart University, said while Koh Tachai was supposed to be protected, the beaches were often overrun with tourists.

"A beach on the island can hold up to 70 people," he said. "But sometimes the number of tourists was well over 1,000 on the beach, which was already crowded with food stalls and tour boats. This caused the island to quickly deteriorate. If it's not closed now, we'll lose Koh Tachai permanently."

Thai authorities warned tourists to look out for any tour companies that might still try to sell trips to the island.

Tunya Netithammakul, director general of Thailand's Department of National Parks, Wildlife and Plants Conservation, said: "Thanks to its beauty, Koh Tachai has become a popular tourist site for both Thai and foreign tourists. This has resulted in overcrowding and the degradation of natural resources and the environment. We have to close it to allow the rehabilitation of the environment both on the island and in the sea without being disturbed by tourism activities before the damage is beyond repair."

In 1999, one of the national park's most popular dive sites, Fantasy Reef, was permanently closed to visitors after its condition deteriorated significantly.