Haiji-1, Asia's first 300-meter deepwater jacket designed and built independently by China National Offshore Oil Corp, had its platform's main body successfully installed offshore in the South China Sea, operator CNOOC said on Monday.

It marks a breakthrough in the country's design, construction and installation technology of ultra-large offshore oil and gas platform jackets, CNOOC said in a statement.

The installation will further guarantee the country's energy security by boosting offshore oil and gas production and is expected to create a new mode for the country's medium and deep-sea oil and gas resource development, the country's top offshore oil and gas producer said.

Deepwater jackets serve as foundations for offshore oil and gas platforms. Used to support the massive weight of an offshore platform, they are the most widely used offshore oil and gas engineering module globally. Construction on the jacket was completed in Zhuhai, Guangdong province, on March 1 and the finished product was successfully hauled onto a barge on March 15.

The installation of the jacket is a major breakthrough, as it is the first time China has installed a fixed jacket some 300 meters underwater. It is also a milestone in the construction of super large offshore oil and gas platforms in China, the company added.