At least three, and perhaps all, of the 15-man crew of a merchant vessel that sank last week while being held by Somali pirates are alive, their families said Saturday.

The Malaysian-flagged MV Albedo container ship, seized by Somali pirates in November 2010, sank last week in rough seas a short distance offshore from the pirate-held town of Hobyo, on central Somalia's Indian Ocean coast.

The Albedo had more than 20 crew from several nations including Pakistan, Bangladesh, Sri Lanka and Iran on board when it was captured, but seven Pakistani sailors were released last August.

While initially the crew were feared drowned, three have since been allowed to call their families, saying that 11 in total of the crew are alive, while four more are unaccounted for.

Begging for their release, families called on the pirates to let surviving crew members go, saying that now that the boat had sunk, its owners had no interest in paying ransom for its release.

"We appealed to everyone in this world to pay money towards the release of our people, but no one listened," they said in a written appeal to the pirates.

"We are very poor people, we even do not have any money to pay for medicines, school fees, buy food for our children."

"Now, that the vessel has sunk... the owner has no interest to pay money and rescue the crew," they added.

"At least release them on humanitarian grounds, else they will die in your hands."

Pirates had initially claimed the crew had drowned, but later lifeboats from the Albedo were spotted onshore.

However, it is understood the sailors were transferred to another pirated vessel, a fishing boat called FV Nahem 3, which is tethered to the sunken hulk of the Albedo.

John Steed, head of an internationally-backed liason body, the Secretariat for Regional Maritime Security, said the crew and pirates on the Nahem are also in danger of sinking.

"We have told the pirates that the best scenario is for them to leave FV Naham 3, and allow us to arrange to recover the hostages," Steed said.

Pirate attacks have been launched as far as 3,655 kilometres from the Somali coast in the Indian Ocean.

But in recent years, international naval patrols from China, Europe, United States and Russia have protected shipping and fought off pirate vessels, with the rate of attacks tumbling by 80 percent from 2011 to 2012, according to the European naval force for Somalia.