Photo taken on May 7, 2012 shows the sixth-generation semi-submersible CNOOC 981 at the South China Sea in China, 320 kilometers southeast of Hong Kong, south China. The CNOOC 981 will begin operations in a sea area at a water depth of 1,500 meters, China National Offshore Oil Corp. (CNOOC) said in a press release. This is the first deep-water drilling rig developed in China. [Photo: Xinhua/Jin Liangkuai]

Workers are seen as a helicopter land on the sixth-generation semi-submersible CNOOC 981 at the South China Sea, 320 kilometers southeast of Hong Kong, south China, May 7, 2012. The CNOOC 981 will begin operations in a sea area at a water depth of 1,500 meters, China National Offshore Oil Corp. (CNOOC) said in a press release. This is the first deep-water drilling rig developed in China. (Xinhua/Jin Liangkuai)

Photo taken on May 7, 2012 shows the sixth-generation semi-submersible CNOOC 981 at the South China Sea, 320 kilometers southeast of Hong Kong, south China. The CNOOC 981 will begin operations in a sea area at a water depth of 1,500 meters, China National Offshore Oil Corp. (CNOOC) said in a press release. This is the first deep-water drilling rig developed in China. (Xinhua/Jin Liangkuai)

BEIJING, May 7 (Xinhua) -- The first deep-water drilling rig developed in China will be put into service in the South China Sea on Wednesday, the country's largest offshore oil producer said Monday.

The sixth-generation semi-submersible CNOOC 981 will begin operations in a sea area 320 kilometers southeast of Hong Kong at a water depth of 1,500 meters, China National Offshore Oil Corp. (CNOOC) said in a press release.

It will be the first independent deep-water oil drilling by a Chinese company, marking "a substantial step" made by the country's deep-sea oil industry, CNOOC said.

About 70 percent of oil and gas reserves in the resource-rich South China Sea is contained in 1.54 million square km of deep-water regions, or sea areas with depths of over 300 meters.

However, most of China's current offshore oil exploration is conducted less than 300 meters below the surface.

The South China Sea is estimated to have 23 billion to 30 billion tonnes of oil and 16 trillion cubic meters of natural gas, accounting for one-third of China's total oil and gas resources.