Malaysian authorities arrested 25 Vietnamese fishers on three boats in separate raids on Thursday, The New Straits Times reported.
A patrol team of the Maritime Enforcement Agency (MMEA) seized the boats, fishing equipment and catch worth RM2.4 million (US$600).
According to the report, the patrol team spotted the boats around 61-70 nautical miles off Kuala Terengganu at 11:17 a.m. on Thursday.
He said 25 crew members, aged between 26 and 42, were found without valid documents.
"Initial investigations revealed that all the crew members in the three boats were carrying out illegal fishing activities in our waters," MMEA chief Zainol Abidin Jusoh said.
He said all those detained are being investigated under the Fisheries Act 1985.
MMEA also arrested 42 Vietnamese fishers and seized three boats in two raids some 51 nautical miles off Kuala Terengganu on March 10 and 11. More than 8 tons of catch worth more than $48,000 were confiscated.