Just one of a group of 30 missing seamen has been found alive after the HTMS Sukhothai went down late on Sunday when it was knocked over by four-metre waves and strong winds.
Six were found dead.
The United States-made corvette was carrying 105 military personnel, many of who were rescued as or soon after it sank, while others had to abandon ship without life jackets and went missing in rough seas.
The navy and air force mobilised five planes, six helicopters and at least four warships to find the missing sailors.
"We expect to find more (of the missing) today ... We are not able to predict if those found will be alive," navy spokesperson Admiral Pogkrong Monthardpalin told broadcaster ThaiPBS, adding weather conditions and visibility had improved.
The vessel sank about 20 nautical miles from the coast of Prachuap Khiri Khan province.
Authorities expanded the search area on Wednesday to cover 40 sq km, Pogkrong said.
The navy said on Twitter search efforts were focused on the area where others had been found on Tuesday.
Families awaited news at rescue centres onshore but some were already grieving as rescue teams flew in the recovered bodies.
"I want them (the navy) to take care of all the soldiers like their own family," said Nawarat Phobat, sister of a deceased marine.
"I don't want to see any more losses in this kind of incident again."
Separately, there were also concerns that damage to the HTMS Sukhothai, which had been in service since 1987, could cause its fuel to spill into the Gulf of Thailand, navy spokesperson Pogkrong said.
"We are closely monitoring the area of the ship and so far there has been no leakage," he said, adding a team was being assembled to safely salvage the ship.
Military accidents in Thailand usually involve aircraft and wrecks of Thai ships are rare.Â
Including the HTMS Sukhothai, Thailand's navy has lost four warships in the 116 years since it was founded.
