Asia's largest refiner Sinopec has agreed to purchase a 50 percent stake in the Shanghai SECCO Petrochemical Company Limited from BP, the company announced on Thursday evening.

Gaoqiao Petrochemical Co Ltd, a 100% subsidiary of China Petroleum & Chemical Corporation (Sinopec), has agreed to buy the 50 percent stake for $1.68 billion.

ECCO is currently owned by BP( 50 percent), SINOPEC (30 percent) and Sinopec Shanghai Petrochemical Company Limited (20 percent), in which Sinopec holds a majority interest.

After the acquisition, ECCO will be owned by Sinopec( 30 percent), Sinopec Shanghai Petrochemical Company Limited(20 percent) and Gaoqiao Petrochemical Co Ltd(50 percent).

According to Sinopec, the company planned to spend 200 billion yuan between last year and 2020 to form four "world-class" integrated refining and chemical production bases in Shanghai, Nanjing, Zhenhai in Zhejiang province, and Maoming and Zhanjiang in western Guangdong province.

The petrochemical company in Shanghai will boost the company’s refining performance in the Shanghai region, it said.

Vice chairman Dai Houliang said the overall refining and chemical capacity of the company will be maintained, amid industry-wide over-capacity.

SECCO is a major producer of olefins, polymers and other derivatives including polyethylene, polypropylene, acrylonitrile styrene, polystyrene, butadiene and other products, according to its website.

The transaction is subject to a number of regulatory approvals and other conditions, and is expected to be completed before end of year.