Thai authorities have rounded up four Vietnamese fishing vessels and detained 35 crew members caught trawling in Thai waters 100 nautical miles off the coast of Songkhla province.

Two Vietnamese fishing boats with their 11 crew members were escorted back to the shore of Songkhla's Muang district on Thursday to face prosecution for allegedly fishing in Thai waters, said the director of the Fisheries Department's Prevention and Suppression Centre in Songkhla, Charoen Omanee.