KUALA LUMPUR (Reuters) - Malaysia on Wednesday (Aug 30) for the first time set fire to a foreign boat for fishing illegally in its waters as it turns up the heat on trespassing trawlers.

Porous maritime borders are a constant problem for Malaysia and its Southeast Asian neighbours, which struggle to keep foreign fishing vessels from operating illegally in their waters.

In early 2016, more than 100 Chinese fishing vessels were detected off the Borneo state of Sarawak, while in April Indonesia sank 81 mostly foreign boats caught illegally fishing in its waters.

The boat was set fire at sea off the coast of the northern state of Kelantan, the first time Malaysian authorities have resorted to such action, according to the Malaysian Maritime Enforcement Agency (MMEA).

The MMEA did not specify the boat's country of origin, but they are believed to be from Vietnam.

"This method shows how seriously the MMEA views incursions by foreign fishing boats in Malaysian waters," the MMEA's Deputy Director-General of Operations, Mohd Taha Ibrahim, said in a statement.

Mohd Taha said Malaysian authorities had so far sunk 285 foreign fishing vessels nationwide to create artificial reefs, but said the method has not made a "deep impact" on foreign fishermen operating illegally in Malaysian waters.

"The MMEA will continue to ramp up our surveillance and patrols to clamp down on crimes committed out at sea," Mohd Taha said.