"Haiyang Shiyou 981 has moved north-west to China's Hainan Island," Major General Nguyen Quang Dam, commander of the Vietnamese Coast Guard, told dpa.
Le Ha, deputy director of Vietnam Fisheries Resources Surveillance Department, said the oil rig was moved more than 40 nautical miles from its former location, and all escort vessels have been removed from the area.
China's official Xinhua news agency said the rig was moved due to the onset of the storm season.
Beijing deployed it in early May, saying at that time that it would be withdrawn on August 15 to avoid the storm season.
DPA