This is the dramatic moment tourists were rescued from a sinking boat off an island in Thailand.

Video shows navy officers helping the stranded backpackers onto a speedboat after their vessel capsized off Koh Bida island in southern Krabi province on December 15.

Boat operator Ekkapak Nongtrut said he had been ferrying 10 tourists to a diving site when their vessel, the Pladao Trip, began taking on water amid choppy seas.

All passengers were safely returned to shore, but the boat was completely submerged underwater.

Chaiyapruek Weerawong, chief of the Mu Koh Lanta National Park where the capsizing occurred, said: 'The boat that sank was a medium-sized diving boat 45 feet (13.5 metres) long and 10 feet (three metres) wide, with a capacity of up to 24 people.

'Water entered the boat's exhaust pipe and caused it to capsize. The tourists boarded a passing boat before officials were called to rescue them.'

Authorities have dispatched divers and local fisherman to the site to search for the sunken boat. The location was marked by an oil slick on the surface of the water.

However, poor weather and strong waves have hampered the search.

The Thai Meteorological Department (TMD) raised a warning for 'heavy to very heavy' rainfall in southern Thailand from December 13 to 16. 

The department said a strengthening northeast monsoon would prevail over the Gulf of Thailand and the south. A low-pressure cell over the lower southern region and Malaysia was forecasted to towards the Andaman Sea from December 13 to 15, causing even more rain.  

Strong winds were expected to churn waves up to 10ft in the Gulf.

Residents near waterways and low-lying areas were urged to be vigilant of flash floods.