A pair of naval gunboats intercepted a fishing vessel carrying 1.5 tonnes of methamphetamine hydrochloride off the coast of main island Luzon just before dawn, Commodore Edward de Sagon told a press conference.

Four people, including one foreigner, were arrested in the joint operation with the Philippine Drug Enforcement Agency, according to de Sagon.

"We still don't have the details of where (the drugs originated)," he said, saying they believed the haul had been transferred from a larger vessel to the fishing ship.

"That was when it was intercepted. There was information and (manoeuvres) that made us suspicious," de Sagon said.

Meth, known locally as shabu, is the most prevalent illegal drug in the Philippines.

"This is one of the largest illegal drug apprehensions in the history of the Philippine Navy," navy spokesman John Percie Alcos said in a statement.

Earlier this month, a large volume of drugs was found adrift just north of the area where Wednesday's arrests were made.

The Philippines' biggest-ever drug seizure came in April last year when more than two tonnes of meth was seized at a police checkpoint on a road in Batangas province south of the capital, according to the presidential palace.