All 21 Indian crew members held hostage by Somali pirates on a chemical oil tanker since August have been released safely, officials in Mumbai said.

The release of the crew on the MV Fairchem Bogey comes after 17 Indian sailors were among hostages freed from a hijacked Italian vessel late last month after more than 10 months in captivity.

"All the 21 sailors are safe and the ship is now on its way to a safe port," Director General of Shipping S.B. Agnihotri told reporters in Mumbai late Saturday.

He declined to comment on reports that a ransom had been paid, but added that 22 Indian sailors remained held by Somali pirates on various other ships in the Indian Ocean.

The Marshall Island-flagged Fairchem Bogey, run by Anglo-Eastern Ship Management, was hijacked when at anchor in Salalah port off the coast of Oman on August 20.

Piracy for ransom is an organised and lucrative operation in Somalia that has expanded into a vast area off the country's coast.