Pirates have seized a tanker off Madagascar in the Indian Ocean and are sailing it towards the Somali coast.
The UBT Ocean was carrying oil from the United Arab Emirates to Tanzania, Svenn Pedersen, of owners Brovigtank, told Reuters.
Piracy has made the seas off the Horn of Africa among the most dangerous in the world, despite naval patrols.
Attacks usually increase between March and May when the seas are calmer.
Mr Pedersen said the owners had received a call from the captain who said there were pirates on board the ship.
"Very quickly afterwards we lost all contact with the boat," he said.
The UBT Ocean is registered in the Marshall Islands.
Its seizure comes two days after pirates captured a Saudi tanker and its crew in the Gulf of Aden and sailed it to the Somali town of Garacad.
An international naval force is patrolling the Gulf of Aden and the Indian Ocean but has been unable to stop attacks on shipping from pirates based in Somalia.
War-ravaged Somalia has had no functioning government since 1991.