China's top economic planner has approved South Korea's SK Group taking a 35% stake in a $2.7 billion petrochemical complex that state refiner Sinopec built in central China, a government statement said on Wednesday.

China's National Development & Reform Commission has approved SK's acquisition of a stake in the complex in Hubei province that has a capacity of 800,000 tons per year (tpy) of ethylene.

The plant is now a joint venture between the Chinese state oil major and SK, with a 65-35 split, NDRC said on its website.

The two companies signed a preliminary deal in December 2011 to explore joint investment in the project. SK's investment cost for the stake was not given.

Sinopec completed building the complex around the end of 2012 in the central Chinese city of Wuhan.

China imports about half its ethylene needs and is keen to reduce that amount. It plans to add a total of about 7.5 million tpy of ethylene capacity between 2011 and 2015.

Sinopec is the industry leader and produces about two-thirds of China's ethylene, a key building block for petrochemicals from plastics to rubber to fibre, and is widely used in the construction, automobile and textile industries.