Pirates robbed a Japanese chemical tanker in the South China Sea on Sunday amid a "serious escalation" of attacks, a maritime watchdog said on Monday.
The International Maritime Bureau (IMB) said pirates armed with knives and steel rods boarded the ship off Mangkai Island in Indonesia last week, stole cash and belongings and fled.
The ship was sailing from Singapore to China and none of its 23 crew were hurt.
The South China Sea is close to the Malacca Strait, a key shipping lane for world trade that more than 50,000 merchant ships ply every year.
"This is the second serious escalation of piracy attacks in the area after the first in June. Ships are being attacked every other day for the past 20 days," said Noel Choong, who heads the IMB's Kuala Lumpur-based piracy reporting centre.
Choong said pirates have struck 27 times in the area since February.
In June, the IMB issued a piracy warning to ships in the South China Sea after a sharp increase in attacks off the islands of Mangkai, Anambas and Natuna.
The number of attacks dropped after increased patrols by the Indonesian navy, but rose again recently.
Choong said the IMB has requested that naval patrols be stepped up again in the area and advised all ships passing in the area to stay at least 45 nautical miles (83 km) from Mangkai Island.
ReutersLast Mod: 06 Eylül 2010, 15:06