Liu Hu became widely known more than 10 years ago for his reports on graft among high-profile figures in the Chinese Communist Party and government.

Police in the southwestern city of Chengdu said late Monday that two men, a 50-year-old surnamed Liu and a 34-year-old surnamed Wu, were under investigation on suspicion of spreading "false accusations" and conducting "illegal business operations".

They have been placed under "criminal coercive measures", according to a police statement, using a euphemism for detention.

While the police only gave their surnames, several Chinese media outlets and Reporters Without Borders (RSF) identified the two men as Liu Hu and Wu Yingjiao, another journalist.

"This case highlights just how restrictive and hostile China has become toward independent reporting," RSF's Taipei-based advocacy manager Aleksandra Bielakowska said in a statement to AFP.

"Anyone who dares to investigate malpractice by the Chinese regime is swiftly persecuted by the authorities," she added.

Liu and Wu recently published an article online alleging corruption by Pu Fayou, the Communist Party secretary of Pujiang county in Sichuan province, and other county officials.

The article, titled "The Sichuan county party secretary who once drove a professor to death, is now driving investment enterprises to bankruptcy", no longer appears on the public WeChat account associated with Liu.

Liu was previously arrested in 2013 for alleged defamation, though the charges were later dropped.

A screenshot of a text message conversation between Liu and someone claiming to be from the Chengdu Commission for Discipline Inspection -- a body tasked with investigating corruption and misconduct allegations -- circulated online since his detention.

The message reminded Liu to report complaints through legal channels.

The reply, supposedly from Liu, said the article "wasn't a tip-off nor was it a petition, so there is no need for your office's reminder".

China ranks 178th out of 180 countries in the RSF Press Freedom Index and is currently the world's largest jailer of journalists, according to the rights group.

"Under Xi Jinping's leadership, control over information has tightened to near-totalitarian levels, with independent journalists treated as a threat to the state", Bielakowska said.