The Cook Islands only barge, Waimarie, has sunk off Mauke after starting to fill with water on its way to Atiu.
Cook Islands Towage director Malcolm Sword says the barge had arrived in Mauke in 'perfect conditions' and offloaded containers and cargo without any difficulties.
But he says that about nine kilometres out of Mauke, the barge began encountering problems, with the crew of the towing vessel Tirotu II noticing it wasn't 'sitting correctly'.
Mr Sword says they activated safety procedures and tried to tow the barge back to Mauke, but he says it was night time by then and a bit dangerous, so they cut the tow line and the Waimarie sank.
It's thought the barge may have hit a large floating object such as a partially submerged shipping container.