The Indonesian authorities said a boat carrying a record 1.6 tonnes of crystal methamphetamine that it had intercepted near the Riau Islands on Tuesday was falsely flying the Singapore flag.

It was the second drug-loaded vessel caught this month by Indonesia to be falsely flying a Singapore flag.

Tuesday's capture took place at 2am near Helen Mar Reef, in the vicinity of the Singapore Strait, by an Indonesian maritime police and Customs office joint patrol.

The fishing boat came from Taiwan and was carrying crystal methamphetamine in rice sacks. All four crew members are Chinese nationals, according to a statement from the police and Customs office.

"The drugs were stuffed in 81 rice sacks and each sack contained 20kg," the statement said, listing the names of the Chinese nationals.

On Feb 7, the Indonesian navy captured a Singapore-flagged fishing boat loaded with one tonne of crystal methamphetamine in 41 rice sacks off the waters of Batam.

The crew of four Taiwanese could not show proper vessel registration documents and a Taiwanese flag was also discovered on board.

Responding to that seizure, Singapore's Central Narcotics Bureau said on Feb 12: "The boat is not a Singapore-registered boat. It is registered in Kaoshiung, Taiwan, as Shun De Man No. 66. Preliminary investigations by the Indonesian authorities show that at the time of interception, the Taiwanese syndicate had used the fictitious name Sunrise Glory for the boat and falsely flown the Singapore flag."

The crackdown on trafficking by Indonesia comes amid soaring consumption of illicit narcotics.

In January, Indonesian police and Customs officers intercepted a 66kg shipment of methamphetamine, known by its street names of shabu-shabu or Ice.

Indonesia has some of the world's toughest drug laws and is one of 33 countries that enforce capital punishment for drug-related offences. But the country has struggled to contain the drug problem.