The men, aged between 20 and 50, were arrested some 80 nautical miles off the northern coastal city of Kuching in Sarawak State on Saturday, deputy director-general of the Malaysian Maritime Enforcement Agency (MMEA), Commander Hamiludin Che Awang, was quoted as saying by the Straits Times.

They were fishing illegally when a patrol ship found them, and they failed to produce a permit or valid personal documents, he said.

All of them have been taken to the Abang Salahuddin Maritime Complex in Kuching for further investigation, he added.

The Vietnamese embassy in Malaysia has confirmed their detention, Tuoi Tre newspaper reported.

The MMEA also seized three tons of fish and fishing equipment worth RM2 million ($480,000) from the two vessels.

The Fisheries Act levies a fine not exceeding RM1 million for the skipper and not exceeding RM100,000 for each crew member or a jail term not exceeding two years for harmful alteration of fish habitat.

There is no official information about when the trial will be held.

This is the fourth time a foreign vessel has been seized for illegal fishing in Malaysian waters this year and all have been Vietnamese.

Vietnamese fishermen are often charged with violations in neighboring countries’ waters.

In 2018 and until April this year there have been 101 cases of Vietnamese boats intruding into waters of other countries in the region. A total of 163 vessels and 1,258 fishermen were 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 to other countries also said they face threats from Chinese vessels that are illegally anchored in Vietnamese waters for trawling and are chased away by them.