A top Chinese anti-corruption official has warned against detaining whistleblowers, reports said Wednesday, amid concern that local bureaucrats are derailing Beijing's efforts to project a graft-busting image.

Chinese citizens with grievances can present their concerns to higher authorities in the form of petitions, a centuries old system of redress that was developed under imperial rule, but many are intercepted before being able to do so.

The state-run China Daily newspaper reported Zhang Shaolong, a senior official at the Central Commission for Discipline Inspection (CCDI), as saying that petitioners should receive a warm welcome from anti-corruption agencies.

He emphasised that there is a legal channel for petitioners to submit whistleblowing materials face-to-face to the anti-graft authorities, the newspaper said, according to indirect quotes.

Zhang was cited as saying detentions at petition offices and public venues were not allowed -- leaving open whether intercepting a petitioner in a non-public place would be acceptable.

China has made fighting corruption a key aim, with President Xi Jinping telling the CCDI -- the ruling Communist Party's internal corruption watchdog and a powerful internal organ -- that there would be "no leniency" against wrongdoing.

Xi has said that corruption could "kill" the party.

Zhang said that 41.8 percent of the cases investigated by the CCDI last year stemmed from public whistleblowers through Internet reports, letters and calls, the China Daily reported.

But many petitioners going to Beijing to air concerns over graft have been detained after they arrived in China's capital by officials from their home provinces, who sometimes employ thugs to make the interception.

"Under the administrative mechanism in most places, the leading officials will not get promoted if too many petitioners appeal to higher authorities," the China Daily noted.

The heavy-handed tactics are said by critics to inflame public anger and undermine the government's legitimacy.

Ahead of China's parliamentary meeting in March the Chinese Human Rights Defenders, an activist network, said that "countless" petitioners had been searched, assaulted and detained, with many forcibly returned to their home towns.

In February, 10 people who detained citizens trying to lodge complaints against authorities were sent to prison, in a rare gesture towards upholding petitioners' rights.