Vietnam has condemned the operation of a Chinese deep-water drilling rig,
called the Haiyang Shiyou 981, as illegal.
The US$1 billion rig, owned by China's state-run CNOOC oil company, was drilling 320 km south of Hong Kong.
On Sunday, Vietnam's Foreign Ministry spokesman said the oil rig was some 120 nautical miles (~220 kilometers) off its eastern coast, Reuters reported.
China. who claims almost the entire oil- and gas-rich South China Sea, rejecting rival claims to parts of it from Vietnam, the Philippines, Taiwan, Malaysia and Brunei, considers considers the oil rig location within its territorial water claims.
China's Maritime Safety Administration announced on Saturday that all vessels should keep 1.6 km away from the rig.
On Sunday, Vietnam's Foreign Ministry spokesman objected to the Chinese announcement saying that Vietnam considers the oil rig is in its exclusive economic zone, Irrawaddy reported.
On Monday China expanded the distance from 1.6 to 4.8 km.
According to Reuters, China routinely sends patrols in the South China Sea but the positioning of such a large structure in disputed waters is seen by some analysts as able to trigger an escalation in the dispute and a "potentially very dangerous scenario."
