In a six-minute news story aired on Monday morning, state broadcaster CCTV showed a visibly nervous and contrite Wang Xiaolu, a journalist with respected financial magazine Caijing, deliver a statement that underlined the yawning chasm between a free press and China's expectations of its state-controlled media.

"I, through private inquiries, these sorts of abnormal channels, obtained news materials," Wang said. "And then through adding my own subjective judgement, I wrote this news report. During a sensitive period, I should not have published a report which had such a huge negative impact on the sharemarket."

It may sound like he was trying to do his job, but Wang's crime, in the eyes of the Chinese state, was that he strayed from the party line.

At a time when China's leaders were under huge public pressure to steady a teetering sharemarket, Wang published a cut-through piece on how Chinese regulators were contemplating pulling back on its emergency intervention measures.

Official news agency Xinhua said Wang had written about the Chinese stock market "based on hearsay and his own subjective guesses" that "inflicted huge losses on the country and investors".

Wang was first taken in for questioning last week, and was officially detained on Sunday.

"I regret my actions, and I am willing to confess my criminal behaviour," Wang said in the CCTV broadcast. "I hope the judiciary can give me a chance and provide me with lenient treatment."

Four executives of CITIC Securities, China's largest brokerage, and one employee of the securities regulator also confessed to crimes including insider trading and fraud.

China's leaders face an uphill battle to rein in irate public sentiment over its accountability and handling of a $US5 trillion ($7 trillion) stock rout and the deadly Tianjin chemical warehouse blasts.

Both incidents prompted wide and often critical reportage from pockets of China's more independent-minded commercial media outlets, who frequently navigate the grey area between serving their readers' interests - and thereby staying relevant and commercially viable - while not straying beyond the government's red lines.

But Chinese authorities are now sending a message. Law enforcement officials said on Sunday they have disciplined nearly 200 people for spreading "rumours" online in connection with recent "major news events".

The government crackdown on politically sensitive discourse targeted people spreading false internet rumours regarding the stock-market turmoil and the Tianjin explosions, the Ministry of Public Security said.

The ministry said the accused had expressed remorse for their actions, in which they "misled society and the public, generated and spread fearful sentiment, and even used the opportunity to maliciously concoct rumours to attack [Communist] Party and national leaders."