More than 300 rescue workers from government agencies and private foundations continue to search for bodies near the Sairung and Praisawan waterfalls in the Yantakao district, 680km south of Bangkok.
Most of the victims were swimming below the two waterfalls during a long weekend holiday for the new year Songkran festival, Arnon Manasvanich, Trang's governor, said.
He said: "The search is continuing, but my belief is we might find more bodies of women and children as they couldn't escape in time."
Soralak Thiepwu, deputy chief of the disaster prevention centre, said: "Twenty-eight bodies were retrieved on Saturday before the rescue teams stopped due to darkness, and we found seven more bodies on Sunday morning."
Hit by rocks
"More than 90 per cent of the dead were hit by rocks after they fell in the force of the flash flood," Sinchai Rongdej, hospital director at Yantakhao district where the waterfalls are located, said.
"Almost all of them had wounds on their heads and their faces."
The areas at the bases of the waterfalls' cascades serve as recreational parks, where people can swim in the normally shallow, rocky streams in the cooling shade of the forests.
Such sites were more crowded than usual at the weekend because Thailand is celebrating its traditional new year, a holiday which extends over about a week and sees many people going to the countryside.