Thailand's military mobilised helicopters, warships and unmanned drones off its central coast on Tuesday as rescue teams raced against time to find survivors after a corvette sank at the weekend in choppy waters.

One marine was rescued on Tuesday from the waters of the Gulf of Thailand, the navy said, among dozens who were forced to abandon the HTMS Sukhothai late on Sunday, after it was knocked over by four-metre (13 ft) waves and strong winds.

There were 29 marines still unaccounted for by Tuesday afternoon. Some were without life vests.

The vessel suffered an engine malfunction as it took on water and went down about 20 nautical miles off Prachuap Khiri Khan province. The U.S.-made corvette, in use since 1987, was carrying 105 military personnel, of whom 76 have been rescued.

Most of those were rescued before the boat sank but dozens had to abandon ship in rafts and life jackets. Vice Admiral Pichai Lorchusakul, the regional navy commander, said finding the men on Tuesday would be critical given their time exposed to the elements.

"Life jacket, life buoy and their floating technique allows us 48 hours to save their lives,” he said late on Monday.

“We will try to do as much as we can to save them.” Helicopters, two unmanned surveillance aircraft, four warships and a C130 transport plane were deployed to find the missing marines, as weather conditions improved.

Lieutenant Colonel Pichitchai Tuannadee, captain of the sunken ship, said he was in the sea for two hours before he scrambled on to a raft and was found by search teams on Monday. ”To see something as small as a life ring or a person's head above the surface of the water, it's very hard to see with the big waves,” he said, adding the missing sailors were likely to be fatigued by now from having to tread water and make sure those without vests stayed afloat. One of the marines was found late on Monday clinging to a buoy.

"He was floating in the water for 10 hours. He was still conscious, so we could take him out of the water safely,” said Captain Kraipich Korawee-Paparwit, commander of the HTMS Kraburi, one of search vessels. Relatives of the missing gathered at rescue centres awaiting news of loved ones. Malinee Pudphong, aunt of a missing marine Saharat Esa said she spoke to her nephew by phone before the boat went down and was shocked to hear he did not get a life jacket.

”We have no hope as they are floating in the sea with just a life ring and with this kind of wind, you think they will withstand that?” she said.

"It's a body of a 21-year-old, he's not strong enough.”