Thai military frigates and helicopters kept up the search late Monday for more than 30 sailors missing after a naval vessel sank, with dozens of others already hauled from the choppy waters.

The HTMS Sukhothai capsized late Sunday as it was patrolling the Gulf of Thailand, about 37 kilometres (22 miles) off the Southeast Asian nation's southeastern coast.

Some sailors survived by jumping into a life raft at night, according to images shared by the Royal Thai Navy, which said 75 people had been rescued.

Late Monday, search and rescue teams continued to scour the waters for the 31 missing sailors, with emergency workers and naval personnel waiting at the windy pier.

The operation involved two Seahawk helicopters, two frigates and one amphibious ship, the navy statement said.

A statement from the Royal Thai Air Force later Monday said they had assisted in the operation, without giving details.

"Our main priority is searching and rescuing as many as we can," naval commander Pichai Lorchusakul said at the pier.

The vessel is believed to have run into trouble after its electronics system was damaged, according to the navy.

"The ship's operating systems stopped working, causing the ship to lose control," a spokesperson said.

Earlier in the day, Prime Minister Prayut Chan-o-Cha said the cause of the incident was being investigated.

"I am following the news closely, about five people are seriously injured," he added in a statement.

The navy said the search was still ongoing over an area measuring around 20 miles by 15 miles, concentrating on a section of sea roughly 18 miles south of the Sukhothai's last position, and the area where the latest survivors were found.

One image shared by the navy showed the vessel capsized, while a video showed a rescue boat alongside the ship in rough waters.