Yin Gang, an expert in international relations at the Chinese Academy of Social Sciences, said the information given by the pirates means they are determined to get a big ransom.

"Sometimes, the pirates just steal from the ships and rob the crew members and leave, but it seems different in this case," said Yin.

In the case of De Xin Hai, the vessel is registered in China and the crew is Chinese.

"It is a State asset, and that might mean more effort from the Chinese side to bring about a rescue," said Yin.

The Chinese escorting fleet in Somali waters is reportedly heading toward the hijacked ship but Huang Xueping, a spokesman with the Ministry of Defense, refused to verify the reports.

Experts said it was more likely that a ransom would be paid than a rescue operation mounted. Ransoms in similar incidents have been from $8 million to $10 million.

"It's better to adopt a non-violent way for the sake of saving lives," said Song Xiaojun, an expert in military studies in Beijing.

The incident has shocked Chinese shippers.

A chief captain with China Shipping Group told China Daily on Tuesday the company has extended its around-the-clock monitoring mechanism to include ships in the Indian Ocean.

"October sees mild wind on the Indian Ocean, which is suitable for Somali pirates to travel far from their home waters with their relatively small vessels," said the chief captain, surnamed Zhang.

Warships in the area primarily provide protection in the narrow and dangerous Gulf of Aden, not in the much larger Indian Ocean.

"The Indian Ocean is too big to defend. It has definitely become a new hotspot for Somalia's pirates," Zhang said.

Reuters and Xin Dingding contributed to the story