KUALA LUMPUR - Seafarers have reported a surge in attacks by armed pirates in a South China Sea shipping lane, an international maritime watchdog said Thursday.

Noel Choong, head of the International Maritime Bureau (IMB) Piracy Reporting Centre, said there had been eight attacks off Indonesia's Mangkai island in the past two weeks.

"It appears one or more groups of pirates are operating in the area. Pirates are armed with guns and machetes and robbed vessels of cash and crew valuables," he told AFP.

Since February the IMB has been informed of 26 attacks in the area, he said, adding that the maritime body had asked Indonesia to beef up patrols to prevent further incidents.

Mangkai island lies on a busy sea passage running along the east coast of the Malaysian peninsula. It is a major route for ships heading between East Asian nations and the Pacific Ocean.

After passing Mangkai they continue into the Malacca Strait, which was once the world's top piracy hotspot. In recent years however attacks there have dropped dramatically, thanks to coordinated patrols by border nations.

Choong said that in the latest incident on Wednesday, six pirates armed with guns, knives and steel rods boarded a Panama-flagged tanker. They stole the cash on board before escaping.

On Monday, pirates boarded a Hong Kong-flagged ship, stripped the vessel of valuables and injured three crew members before escaping.