PetroChina, the nation's largest oil producer, started formal operations at its Dushanzi refinery and chemical plant in far western Xinjiang region Monday to ensure energy security, the refinery said Tuesday.

The plant, which includes a 10 million-tonne-a-year refinery and a 1 million tonne-a year ethylene production facility, is an important part of the China-Kazakhstan energy cooperation strategy.

The facility mainly processes Kazakhstan high sulfur crude pumped via a Kazakhstan-China pipeline.

It covers an area of 455 hectares and has an investment of 30 billion yuan (4.4 billion U.S. dollars).

The plant is expected to have an annual sales revenue of more than 60 billion yuan.