(Yicai Global) Oct. 30 -- Two of China's stock market heavyweights, China Petroleum & Chemical Corp. (Sinopec) [SHA:600028] and major competitor PetroChina Company Ltd. [SHA:601857], have bucked the trend to stay strong during Monday afternoon's trading.

Both firms saw prices rise significantly amid an overall downward trend on the market, despite no obvious reasons for the buying spree.

The two petrochemical giants, with CNY1.51 trillion and CNY722 billion market caps, respectively, are two of the biggest companies on the A-share market, and changes in their share prices can significantly affect the market index.

The two stock traded at a relatively weak position throughout the morning trade but began their upward push as soon as the market resumed in the afternoon.

At 02.00 p.m., Sinopec was up 1.70 percent to CNY5.97, while PetroChina was up 1.85% to CNY8.28.

China's stock markets stabilized slightly after a sharp fall in the early stage of the trading on Monday. The benchmark Shanghai Composite Index was down 0.89% in the afternoon trade.