A Chinese newspaper published a front-page call Wednesday for police to free a journalist detained after reporting "financial problems" at a partly state-owned company, in a rare example of media defying authorities.

The New Express tabloid, based in Guangzhou in the southern province of Guangdong, carried the full-page editorial under the headline "Please release our man" in oversized stark black print.

Its journalist Chen Yongzhou was held on Friday by police on "suspicion of damaging business reputation" after he wrote 15 articles on "financial problems" at Zoomlion, a giant engineering company.

The firm is about 20 percent owned by the state, and is listed on the Hong Kong and Shenzhen stock exchanges with a total market capitalisation of more than $8 billion.

It is one of China's biggest manufacturers of construction machinery, such as bulldozers, and a major tax contributor to Changsha city in the neighbouring province of Hunan.

"We are a small newspaper, but we have the backbone no matter how poor we are," said the editorial, adding it was "ashamed" for not having spoken out earlier due to fears that Chen might be maltreated.

Armed police from Changsha carried out the detention in a "cross-province" operation, the editorial said, adding they were also looking for the paper's economic news director, who has been "hiding out" for several days.

In the published reports Chen accused Zoomlion of providing fraudulent accounting figures such as inflated profit data, according to a posting on the newspaper's account on Sina Weibo, a Chinese equivalent of Twitter.

Zoomlion and its subsidiaries earned more than 12 billion yuan ($2.0 billion) in profits and tax revenues last year, according to the company's website.

"We have always thought that as long as we report in a responsible way, there would be no problem," the editorial said, adding the paper had reviewed Chen's reports and found no significant errors.

"Even if there was a problem... we can go to court and if we lose the case we can pay appropriate compensation, even if it means we have to shut down," it said.

"But the facts showed that we were too naive."

China's media are tightly controlled by the government and it is rare for an outlet to openly confront the authorities.

In a high-profile incident in January, staff at Southern Weekly, a liberal newspaper also based in Guangzhou, went on strike after censors blocked a New Year message in the paper urging greater respect for constitutional rights.

Chen's detention immediately drew high attention on China's social network services Wednesday and was the third hottest topic on Sina Weibo.

Most commentators were sympathetic, with one poster using the handle Li Yaosha, or "little stupid Li", drawing comparisons with state broadcaster CCTV's flagship news programme.

"If New Express journalist Chen Yongzhou is detained... because of that, then why not arrest people at the Evening News, which broadcasts fake news every day?" he wrote.

Yu Jianrong, a government researcher and influential blogger, blasted the detention as "abuse of public power".

Chinese censors apparently moved to contain the impact of the editorial, which was taken down from the home pages of major news portals including Sina and Netease by midday Wednesday.

It is not the first time that journalists from the New Express, which targets middle class readers, have been detained.

In August, Liu Hu, another reporter with the newspaper, was taken away by police after he posted accusations online against a former senior official in Chongqing, the megacity in southwestern China.

Chinese authorities have launched a broad crackdown on "online rumours", with a recent rule saying that Internet users could face three years in prison for writing defamatory messages that are then re-posted 500 times.