A helicopter dropped a $4 million ransom payment on to the deck of a Chinese coal ship hijacked by Somali pirates in mid-October, a pirate source on board the vessel said.

The De Xin Hai and its 25 crew were carrying about 76,000 tonnes of coal from South Africa to the Indian port of Mundra when it was seized by gunmen in the Indian Ocean some 1,100 kilometres east of the Horn of Africa.

Sea gangs from Somalia have made tens of millions of dollars in ransoms by hijacking commercial shipping in the Indian Ocean and the strategic Gulf of Aden that links Europe to Asia.

Patrols in the area by warships from several nations only appear to have forced the pirates to hunt further from shore.

"A helicopter dropped the ransom money onto the ship. We have received $4 million," Hassan, one of the pirates on the De Xin Hai, told Reuters by telephone to cheers in the background.

"We hope to disembark in a few hours. The crew is safe and -- although they will not have their freedom for a few more days -- they are all happy now."

China sent three warships to Somali waters late last year with great fanfare after a ship carrying oil to China was attacked by pirates.

But Chinese warships, like those from other countries, provide protection mainly in the narrow and dangerous Gulf of Aden, not in the much larger Indian Ocean.

- Reuters