A diving boat packed with tourists capsized off the resort island of Phuket on Thursday.
The kingdom is already in the global spotlight for a dramatic rescue mission in the north of the country, after 12 boys and their soccer coach were trapped in a cave complex.
Ambulances could be seen waiting for various people to be rescued.
The bodies of some of the dead were found floating face down in the water, still wearing life jackets, several miles from where the boat sank.
Some 48 passengers and crew members were rescued before the boat sank.
Thai Rescue workers carry the body of a victim on a stretcher, after a boat capsized off the tourist island of Phuket, Thailand, July 6, 2018.More news: Woman Climbs Statue of Liberty to Protest Family Separations, Island Shut Down
The two other missing people were on the boat Senerita, which was carrying 42 people - 35 tourists, five crew, one tour guide and one photographer.
"There were high winds this evening", he said, adding that a weather warning had been issued because of "strong winds and storms" on Wednesday.
A Chinese consular official has arrived at the operations centre in Phuket to monitor the rescue effort.
An investigation has been ordered into why the boats went out, despite severe weather warnings.
The Royal Thai Marine Corps said in a statement that the Phoenix sank about 7km from the shore and the boat had sunk to a depth of about 38-40 metres.
Jin Yilin, consul-general of the Chinese Embassy in Thailand, said a delegation from the Chinese Foreign Ministry is on the way to Thailand.More news: Hague warns Tory rebels not to ‘push too hard’ on Brexit
Twelve bodies were retrieved by the navy, who said "quite a few" bodies had also been found inside the sunken vessel.
The Phoenix was carrying 105 passengers, the majority of whom were Chinese tourists, when it hit trouble, sparking a rescue attempt that took place in the dark.
"All agencies are co-operating in their search at this time", Norraphat said.
One fisherman is still missing after being swept from a Thai fishing boat Thursday near Krabi province.
The Thai incidents came after an overloaded boat carrying illegal Indonesian immigrants capsized in bad weather off Malaysia's southern Johor state late Sunday. Provincial authorities and the 3rd Army are mapping out measures for land, water and air searches for the missing people, " the governor said. Ten others, including four women, were found dead. Rescue operations involving 150 personnel are ongoing for nine people believed to be still missing.More news: Kim, Xi Said to Agree US Troops Should Leave South Korea