The Malaysian Maritime Enforcement Agency (MMEA) said three foreign vessels believed to be Vietnamese were intercepted at around 3 p.m. Tuesday for trespassing into Malaysian waters and carrying out electric pulse fishing off the Sabah coast.

The boats failed to show a license to operate in Malaysian waters. 33 Vietnamese fishermen aged between 16 and 55, including three skippers, were arrested, The Star newspaper reported.

"They also kept prohibited devices used in electric pulse fishing, which threatens Malaysia’s marine ecosystem," an MMEA officer said.

Officers also found 900kg of fish in the three boats.

The detained Vietnamese fishermen and boat skippers will be tried for violating Malaysia’s Fisheries Act.

Vietnamese fishermen are increasingly being caught in waters of neighboring countries.

Since the beginning of 2018 there have been 101 cases of Vietnamese boats allegedly intruding into the waters of other countries.

A total of 163 vessels and 1,258 fishermen have been detained, Nguyen Quang Hung, deputy head of the Directorate of Fisheries under the Ministry of Agriculture and Rural Development, said last month.

Despite its 3,260 km (2,025 miles) coastline, Vietnam is running out of near-shore seafood resources, and some fishermen who have sailed into other countries’ waters also said they face threats from Chinese vessels that are illegally anchored in Vietnamese waters for trawling.