Indonesian authorities have resumed their tough stance against illegal fishing in the country's water by sinking 51 foreign ships.

Maritime and Fisheries Minister Susi Pudjiastuti says the ships were sunk Saturday at five ports across the archipelago, which has some of the world's richest fishing grounds. The boats had been seized from Chinese, Malaysian, Filipino, Thai and Vietnamese fishermen.

The move comes a week after an Indonesian navy ship was rammed by two Vietnamese coast guard vessels after intercepting a boat it says was fishing illegally.

Last year, the ministry sunk 125 mostly foreign vessels, including 86 Vietnamese-flagged ships, 20 Malaysian and 14 from the Philippines.

Indonesia says it has sunk more than 500 illegal fishing vessels since October 2014.