The ship, which was heading for Bangladesh's port of Chittagong, ran into trouble early today in rough seas some 32 kilometres off an island near Phuket in Thailand's south.
Eighteen of the crew were rescued from the ship by a navy helicopter, according to Thammawut Marlaisukarin, a captain in the Thai navy, but ten others were in a lifeboat "that drifted from the site" of the rescue.
The missing crew members had not been located after several hours of searching.
"The ship capsized in rough seas -- there are five-metre high waves in the Andaman Sea near Phuket now," he said.
Phuket is Thailand's biggest island and one of its most popular tourist destinations.