HONG KONG (REUTERS) - A giant Chinese oil rig has finished its first round of drilling in South China Sea waters also claimed by Vietnam and moved to another site in the area, the rig's operator, China Oilfield Services Ltd (COSL), said on Tuesday.

In a statement, COSL said exploration would still take place off the Xisha islands, China's name for the disputed Paracel chain, suggesting the rig was not moving far.

In early May, the rig was deployed between the Paracel islands and the Vietnamese coast, sparking deadly anti-China riots in Vietnam and protests from the government in Hanoi.

The rig had "smoothly" completed the first phase of its work, said COSL, the oil service arm of state-run China National Offshore Oil Company (CNOOC) Group, which owns the US$1 billion (S$1.25 billion) platform.

COSL said it had obtained relevant geological data from the drilling, but did not give details or specify the current location of the rig. Neither officials from COSL nor CNOOC Group could be reached for comment.

In line with previous statements, COSL said drilling was on track to be completed by mid-August.

Vietnam has said the rig is in its 200-nautical mile exclusive economic zone and on its continental shelf. China - which claims almost the entire South China Sea - says the rig is operating within its waters.