About half of the record 285 attacks recorded by the International Maritime Bureau (IMB) last year occurred here, with Indonesia and Malaysia among the worst-hit nations.
Jayant Abhyankar, the deputy director of the IMB, told The Daily Telegraph newspaper that the increase "highlights that modern piracy is violent, bloody and ruthless".
The IMB reported that pirates world-wide in 1999 carried guns on 53 occasions and knives were used twice as often as the previous year.
Gun-battles
Approximately one-third of the world's commercial shipping passes through the South China Sea annually.
Some coastal towns in Malaysia's Sabah state, the scene of Sunday's tourist kidnappings, have been regularly targeted by armed Filipino gangs.
In September 1998, a group of armed pirates killed a fisherman in Bohayan Island in Sabah, took his boat and robbed other fishermen.
A gun-battle followed with pursuing police but the pirates escaped into international waters.
Border patrol co-operation to stem piracy has been a key feature of recent bilateral talks between Malaysia and the Philippines.
Crews murdered
Piracy has come a long way since the days of the cutlass and galleon.
Modern pirates are armed with speedboats, AK-47's and mobile phones.
In a typical attack at least 10 men in high-speed launch will follow a freighter, on which an insider has usually been planted beforehand to provide location and freight details.
Once boarded they will either hijack the ship for its cargo, or, more typically, go straight to the captain's safe, which usually contains tens of thousands of dollars in petty cash.
Sometimes the ship is repainted and given a new name, and false documents are used to create a new identity for the vessel.
Entire crews have also been known to have been kidnapped or murdered.
Last December the Chinese authorities executed 13 Chinese pirates who had been convicted of murdering 23 crew members of the cargo ship Cheung Son, which was seized just outside Hong Kong waters by pirates dressed as Chinese officials.
Photographs showing the drunken pirates celebrating the killing spree were later found by police, although the ship was never found.
The IMB's advice to ships which are being followed is to sail full speed ahead and radio for help.
It urges ships to maintain constant anti-piracy watches, even when in port.