The same day, the Singaporean-flagged Pramoni - a chemical tanker with a crew of 24 - was seized by pirates in the Gulf of Aden, one of the world's busiest waterways.

Harbour said the Asian Glory's crew of 25 - from Ukraine, Bulgaria, India and Romania - appeared to be safe and that the pirates had not yet made contact with the ship's owner, Zodiac Management Agencies.

"The standard procedure for the pirates is to get the ship back to their stronghold and then contact the owner," he said.

"I don't know yet where the ship is bound."

Million-dollar ransoms

Somali pirates have hijacked more than 80 ships in the past two years, with many of the seizures earning the pirates multi-million-dollar ransoms.

Pirates now hold 14 vessels and close to 300 crew members.

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Harbour said the Asian Glory was headed for, but had not yet entered, the internationally recognised travel corridor patrolled by the European Union when it was hijacked.

Officials said the Pramoni was travelling east towards India when it was seized.

The ship's master radioed that the crew - from Indonesia, China, Nigeria and Vietnam - was safe. The vessel is now also heading towards Somalia.

A spokesman for Zodiac confirmed the Asian Glory hijacking and said on Saturday that the crew's families were being notified.

The company said it would limit the information it released out of concern for the crew's safety.

Zodiac also owns a chemical tanker, the St James Park, that was hijacked on Monday.

A statement on the company's website indicated on Saturday that the vessel is now anchored off the coast of Somalia.

Zodiac said it has not yet been contacted by the pirates holding the St James Park and its 26-person crew.

'Needle in a haystack'

Speaking to Al Jazeera on Friday, Simon Jones from Trinton International, a maritime risk and security assessment company, said: "The problem is the area of sea they are trying to protect is so vast ... that [searching for] a few pirates sprinkled around the area ... is like trying to find a needle in a haystack.

"The only realistic way that piracy can be stopped at sea ... is for those vessels to be pratically prepared to prevent piracy occurring, preventing them getting on board and preventing them from getting close to the vessel ... the navies cannot be there all the time.

"You haven't got a blanket requirement by all shipping companies travelling through these dangerous regions or a regulation that requires them to adhere to security requirements."