China's leading oil producer instructed its managers to stabilize production and market supply on Wednesday after four senior managers were investigated on suspicions of "grave discipline violation" earlier this week.

Zhou Jiping, chairman of the China National Petroleum Corporation, said at a meeting on Wednesday that the four managers in the company had been investigated, showing the determination of anti-graft authorities to fight corruption, according to a brief on the company's website.

The company managers and workers should firmly oppose corruption, stabilize production and expand the businesses at the same time, Zhou urged the company's senior managers at the meeting.

Wang Yongchun, vice-president of the company, was investigated for "grave discipline violation" — a term that always refers to corruption, the Central Commission for Discipline Inspection of the Communist Party of China, the country's top anti-graft agency, announced on Monday.

Three other senior managers from the company were also investigated on accusations of grave violations of discipline, according to a statement issued on Tuesday on website of the State-owned Assets Supervision and Administration Commission of the State Council.