"We primarily sprayed chemical substances for the oil to settle down, and we are studying other measures, including pulling up the ship, to solve the situation completely," an official from the Port Authority in Ba Ria-Vung Tau province said.

The official, who declined to be identified, said the ship was 100 metres long and 15 metres wide but that he did not know what it had been carrying.

He said the environmental damage so far was not serious.

"It's from some metres wide and about several kilometres long, which is too tiny to call it a disaster."

Media reports identified the ship as a Malaysian vessel, the Gigekex Tajo, carrying 166 containers, 26 tonnes of diesel oil and 115 tonnes of fuel oil. All 19 crew were rescued and have been repatriated, the reports say.

The port official said those details had not been confirmed.

"They think it's the Malaysian ship as there was one that sank in the area on November 14, 1995 in a fierce storm, but we are yet to have any conclusion," he said.

Rong oil field is located 120 km (74.52 miles) southeast of Ba Ria-Vung Tau province. It is one of the country's key energy resources along with Bach Ho (White Tiger) oil field.