An unusual rock shaped like a boat sail balancing precariously is drawing visitors to a tourist island in Thailand.

The strange 'sail rock' sits on top of a rock formation on Koh Similan, in the Similan Islands archipelago in Phang Nga province.

Visitors queued to take pictures with the lone boulder overlooking the turquoise waters on the island.

Aside from the sail rock, Koh Similan also has other bizarre rocks such as the 'boot rock' and the 'Donald Duck rock.'

Tourists can enjoy the horseshoe-shaped bay, go sunbathing on the white sand beaches, or take dives in the crystal clear sea to observe the colourful corals and marine life underwater.

The island is open to tourists before closing on May 16 for Thailand's rainy monsoon season. It will reopen on October 15.