Police in Shanghai have busted what they say is gang who duped websites into deleting negative reviews by posing as government censors and media personnel.

The gang made 3 million yuan (US$470,000) from the activity before the bust, according to Chinese news site ThePaper.cn.

In late 2016, the gang started advertising its services to companies wanting criticism of their firms scrubbed from the internet, according to Shanghai police.

More from the South China Morning Post:

Chinese man held over 'online dating scam using voice manipulation device'

Chinese market targeted by scammers who set up fake QR codes to divert payments

'They stood us up': White House says it cancelled Kim Jong-un meeting because North Korea refused to talk – despite Donald Trump's earlier claims

Deleting articles for cash is illegal in China but is estimated to be a 100 million yuan industry, according to state-run China Discipline and Supervision News.

The gang was headed by two men who had been charged with running an illegal business and forging government documents and seals, police said.

Once hired, they would contact websites reposting the negative reports, posing as staff from the media organisation that wrote the original articles.

The gang would then send a statement with the source's official seal to request the removal: "We [the media organisation] were alerted by the authorities that the article was not suitable for online distribution as the incident mentioned in the article is under police investigation."

If that failed, the gang would pose as staff from the China Internet Illegal and Unhealthy Information Reporting Centre and order the deletion of the articles, using an email address that was similar to those used by the real agency, police said.

The authorities said the gang had roughly 1,000 articles pulled from the web, charging each company up to 100,000 yuan for its services.

In China, it is not uncommon for companies to pay hackers or website staff to delete negative information posted online. Chinese authorities often also order the removal of certain posts deemed unsuitable, as part of their routine censorship efforts.

But Jiang Shengjie, from the Shanghai Public Security Bureau's cybersecurity unit, said the gang's approach was new.

"In the past, such cases merely involved companies paying directly to remove the articles. We have never encountered such cases where people have posed as media enterprises or government authorities to order the removal of articles," Jiang said.

Wei Wuhui, an assistant professor from Shanghai Jiao Tong University's media school, said the gang flourished because Chinese news portals were used to government intervention in their content.

Some local governments also tried to limit negative reports on key firms, Wei said.

"The companies are key taxpayers in the region and the authorities are keen to protect them," he said. "So it sometimes leaves ordinary citizens confused about whether a government body's order to remove articles is truly a genuine request or not."

Follow CNBC International on Twitter and Facebook.