The two-engine speed boat, travelling between Koh Larn and Pattaya, sank about 100 metres from the shore shortly after departing around 10am, local media reported.
Rescuers managed to save all 27 people aboard the boat. Most of the occupants of the vessel were foreign tourists whose nationalities were not disclosed by the authorities.
Two of the passengers were slightly injured and sent to Pattaya Memorial hospital.
Authorities were investigating the cause of sinking.
