Philippine anti-poaching patrols have detained two Chinese and three Vietnamese fishing vessels along with more than three dozen crew members in the extreme north of the country.
The arrests near tiny islands off the main island of Luzon came as a maritime dispute between Manila and Beijing simmers in the South China Sea.
Coastguard and fisheries officials on Monday said that two Chinese fishing vessels that were fraudulently flying the Philippine flag were detained along with their 25 crew members off the island of Sabtang.
Bureau of Fisheries and Aquatic Resources Director Asis Perez said, the presumption in these types of cases is that they are here to commit illegal fishing.
The vessels were escorted to the port of b=Basco and the crews were held on board as investigators waited for interpreters.
Perez said the bureau and the coast guard also arrested 18 Vietnamese fishermen on three boats for illegally fishing in Philippine waters last week.
He said authorities have asked state prosecutors to file illegal fishing charges against the Vietnamese, who were detained on Thursday off Calayan Island, 122 kilometers (76 miles) south of Sabtang.
Poaching carries a fine of up to 1 million dollars under the Philippine law.