Tourists at Da Nang beaches on January 2 discovered thousands of blobs of oil, which have been washed up along a one-kilometre length of My Khe beach.
According to Phan Minh Hai, deputy head of Son Tra Eco Tourist Sea Board, the oil started to appear on Sunday, but no one is sure where it has come from.
The Management of the Son Tra Eco Tourist Sea and Da Nang beaches has asked the provincial Department of Natural and Resources to collect samples for testing.
Hai said that it was possible that the oil came from passing ships, and had been blown inshore, by the prevailing northeasterly winds.
The board has asked an environmental company to clean up the mess.