The removal of the shows coincides with a broad crackdown on online freedom of expression that has intensified since President Xi Jinping came to power last year and drawn criticism from rights advocates at home and abroad.

Authorities last week also stepped up their battle against pornography, revoking some online publication licenses of one of China's largest Internet firms, Sina Corp, for allowing

"lewd and pornographic" content.

"While ordinary people and governments have enjoyed the conveniences brought by the Internet, they have also in turn experienced the Internet's negative effects and hidden security dangers," the People's Daily, the party's main mouthpiece, said in a commentary.

It was published under the pen name "Zhong Sheng", meaning "Voice of China", often used to give views on foreign policy.

"If you don't have Internet order, how can you have Internet freedom? Anyone enjoying and exercising their Internet rights and freedoms must not harm the public interest and cannot violate laws and regulations and public ethics," the paper said.

Four U.S. television shows, The Big Bang Theory, The Practice, The Good Wife and NCIS, were ordered removed from video websites at the weekend by the government, the official Xinhua news agency said.

The series are all popular and it was not clear why these particular programs had been singled out.

Searches on Youku Tudou, Sohu and Tencent, which provide the shows, produced messages that the content was temporarily unavailable.

"I believe it's a standalone event and it doesn't represent a policy change toward American TV shows," Sohu CEO Charles Zhang told a conference call with reporters.

The directive, he said, gave no explanation for the take-down notice and he declined to comment further. Youku Tudou and Tencent declined comment on the order.

Earlier on Monday, state broadcaster China Central Television (CCTV) told Reuters it had acquired the exclusive broadcasting rights for The Big Bang Theory, but did not specify whether or not the license was only for TV.

TIGHTER REGULATIONS

The removal of the shows followed a directive from the State Administration of Press, Publication, Radio, Film and Television (SARFT) last month that tightened the process forbroadcasting television programs and short films online.

Programs and films lacking licenses are not permitted to be shown online, according to the SARFT directive. Penalties include a warning and a fine and, in serious cases, a five-year ban on operations and investment in online programming.

But there are no specific regulations governing overseas TV programs licensed by Chinese websites, said one person who works at an online video site, adding that regulation was expected at some point but with a minor impact on the industry.

Nonetheless, the lack of clarity from both the government and the companies involved raises questions about whether foreign programs will be subject to greater scrutiny.

China's online video market was worth 12.8 billion yuan ($2.05 billion) in 2013, according to Chinese data firm iResearch. Market value is expected to almost triple by 2017.

SARFT has been in discussions with online video sites about greater control of their content since 2009, according to people familiar with the matter.

China maintains tight control over the media. Censorship is widespread, and Internet users cannot access information about many topics without special software to circumvent restrictions.

Online video sites are extremely popular and can act as a lodestone for comment on social issues.

The Communist Party last year renewed a campaign on online interaction, threatening legal action against people whose perceived rumors on microblogs like Sina Weibo, are reposted more than 500 times or seen by more than 5,000 people.

The campaign has muted online demands from advocates of transparency, who see it as a tool to punish Party critics.