PetroChina Co. opened slightly lower on Wednesday, after its parent company China National Petroleum Corporation (CNPC) refuted the rumor that the chairman of its Shanghai-listed arm was missing.

CNPC, the country's largest oil producer, late Tuesday posted a news release on its website saying that Jiang Jiemin had attended a company meeting on Monday, after rumors spread in cyberspace claiming that Jiang had "mysteriously" disappeared.

The oil giant said in an interview that Jiang, who is also chairman of the CNPC, was admitted to hospital in July for sickness. It said he had been receiving therapy and will soon end the treatment. It added that it is not cancer or any other serious illness.

Jiang, 57, who has been CNPC chairman since 2007, last showed up at a work report meeting held in Chengdu of southwest China's Sichuan Province on Aug. 2, according to news disclosed on CNPC website.

Despite the company's accounts, investors are still worried there might be other reasons for Jiang's absence, as CNPC provided no photograph of his attendance at Monday's meeting.

PetroChina's shares seesawed after opening 0.23 percent lower at 8.76 yuan, with losses once growing to 0.46 percent within an hour of the opening.

Latest reports showed that PetroChina's profits dropped 6 percent from a year earlier to 62.02 billion yuan (9.77 billion U.S. dollars) in the first six months, due to government control over domestic refined oil prices and rising costs.