Tonnes of cocaine are washing up on the Philippine coast in what law enforcers say point to a dramatic rise in the use of drug routes that cross the Pacific from the United States and South America, and a boom in synthetic drug production across South-east Asia.

In the latest incident, seven suspected cocaine bricks were found on Sunday floating near a beach in Mauban town, Quezon province, about 150km south-east of the capital Manila.

Quezon police chief Colonel Ramil Montilla said the stash was worth about 35 million Philippine pesos (S$930,000).

In May, fishermen in Sorsogon province, some 300km further south of Quezon, netted 12 boxes that contained 39 bricks of cocaine with an estimated value of more than 200 million pesos.

Also, in a span of just a week in February, some 472 million pesos worth of cocaine, packed in bricks, were found floating near the coastline in four provinces that face the Pacific Ocean. By the month's end, the haul topped 871 million pesos.

Police have said it is possible the drugs were bound for Australia, where there is strong demand for cocaine.

They believe that, in the past five years, there has been an explosion in the number of boats carrying cocaine and methamphetamines from the US and South America to Australia via the Pacific.

Mr Sanho Tree, a fellow at the Drug Policy Project at the Institute for Policy Studies, a US-based think-tank, told the BBC that boats would toss drugs overboard to destroy evidence if they are being chased. The bricks could also have been part of a shipment lost by smugglers mid-handover. "Sometimes they'll submerge drug packages underwater with a net and anchor for pick-up, but packages can sometimes break free," he said.

Bricks of cocaine have also been found along the waters and coastlines of small Pacific states like Fiji, Vanuatu, Tonga and Papua New Guinea.

Philippine Drug Enforcement Agency spokesman Derrick Carreon, said there has also been a boom in cocaine and meth production across the borders that straddle Laos, Thailand and Myanmar.

Drugs from illicit factories in the infamous Golden Triangle are slipping into the Philippines through waters off the Sulu archipelago and Zamboanga peninsula, he said.

He said the Philippines' vast coastline and porous borders have made it an ideal way station for narcotics that eventually land in Australia, New Zealand and Japan.

Drug agents in the Philippines have also unearthed ties between Chinese drug syndicates and Mexican cartels, said Mr Carreon.

"It's been a standing trend through the years. It's nothing new," he said.