Forty kilometers of the seashore northwest of Haikou, the capital of China's southernmost province of Hainan, has been polluted by oil, reported local fishermen on Tuesday. Provincial and city maritime bureaus are investigating, but the source is still unclear.

According to the Nanguo Metropolis News, it may have collected and been carried on waves from far out at sea before being washed ashore.

The newspaper also reported sources from the city maritime bureau as saying that no new oil patches have been observed in the sea.

The cleanup is underway, and the collected pollutant will be disposed of by environmental protection departments.

It may have come from moving vessels, since docks and oil depots have not been found to have any leaks. Maritime departments are checking entry-exit shipping records and seeking assistance from the neighboring province of Guangdong in efforts to identify the source.

The city environmental protection bureau is closely monitoring the quality of seawater, and at the same time looking for any possible sources of the pollution on land.

The oil has clearly affected the immediate coastal and offshore environment, but consequences for life further inland and at sea need further investigation, said a bureau official.