BEIJING - Vietnam must immediately stop its unilateral oil exploration in disputed areas of the South China Sea, China's Foreign Ministry said on Thursday.

Vietnam expelled Chinese fishing boats from waters near China's southern Hainan province, Foreign Ministry spokesman Hong Lei said at a regular briefing on Thursday.

It was not immediately clear when the incident took place.

The vast waters of the South China Sea are rich in oil and gas and are contested by China, Vietnam, the Philippines, while Taiwan, Malaysia and Brunei also lay claims to parts of it.

Last Friday a Vietnamese ship in the waters had a cable it was pulling cut by two Chinese fishing ships.