Chinese oil giant Sinopec, Asia's largest refiner, has reported a 12 percent gain in net profit for the first half this year, thanks to strong growth in the world's second largest economy.

Sinopec earned 41.2 billion yuan ($6.4 billion) in the first six months, up from 36.8 billion yuan the same period a year earlier, according to financial results filed with the Shanghai Stock Exchange.

Total revenue rose 31.5 percent on the year to 1.23 billion yuan in the first half. Sales of petroleum products, which accounted for more than 60 percent of total revenue, surged 31.6 percent to 746.3 billion yuan.

"The Chinese economy has continued its steady and robust growth," the company said in the statement late Sunday. "Demand for petroleum and petrochemical products has increased steadily."

China's economy grew an annual 9.6 percent in the first half of this year.

Sinopec said international and domestic prices of crude oil, refined oil products and petrochemical products all increased in the first half, helping the company.

But it said it would keep an eye on volatility in crude prices in the second half of this year.

"We expect international crude oil prices will fluctuate within a wider range," Sinopec said, but added domestic demand for its refined oil and chemical products would stay steady.

The company produced 156 million barrels of crude oil in the first half, down 5.4 percent from a year earlier, due to the overhaul of production machinery at a field in Angola.

Its natural gas output rose 26.6 percent year on year in the first half to 253.9 billion cubic feet.

In the second half of this year, Sinopec said it plans to produce 165 million barrels of crude oil and 247.2 billion cubic feet of natural gas.