Thai navy ships and helicopters are searching for more than 30 sailors still missing more than 17 hours after their warship sank in rough seas in the Gulf of Thailand.

As of Monday afternoon, 75 sailors from the HTMS Sukhothai corvette had been rescued and 31 were still missing, the navy said.

One sailor told Thai Rath television that there were not enough life jackets because more people than usual were aboard the ship.

In comments broadcast by another station, PPTV, Navy Commander Admiral Choengchai Chomchoengpaet confirmed that was true.

“This operation, they added staff from the Marine Corps and Air and Coastal Defence Command, about 30 people. This is why I think there were not enough life jackets,” he said.

The ship normally carried a total of 87 crew and officers, according to the navy’s website.

The high waves that caused the accident had lessened since Sunday night’s sinking, but were still high enough to endanger small boats, the navy said.

A rescued crew member interviewed by Thai PBS television said he had to float in the sea for three hours before he was picked up.

He said the ship was buffeted by waves 10ft high as it was sinking, complicating rescue efforts.

“The waves are still high and we cannot search for them from the horizontal line. We have to fly the helicopters and search for them from a bird’s eye view instead,” navy spokesman Admiral Pokkrong Monthatphalin told Thai PBS.

Eleven of the rescued sailors were treated in hospital. The navy denied a local media report that one death had been confirmed, saying that fatality was a result of an accident involving another boat.

Strong winds blew seawater onto the HTMS Sukhothai and knocked out its electrical system on Sunday evening, making control of the ship difficult.

The navy dispatched three frigates and two helicopters with mobile pumping machines to try to assist the disabled ship by removing the seawater, but could not do so because of the strong winds.

The loss of power allowed more seawater to flow into the vessel, causing it to list and sink.

Thailand’s Meteorological Department had issued a weather advisory for the general area just a few hours before the accident, saying that waves in the Gulf of Thailand were expected to be 7-14ft high with thundershowers.

It suggested that all ships “proceed with caution” and warned small craft not to go to sea until Tuesday.