Movie fans were surprised recently when they visited popular websites that offer free entertainment downloads and found them closed by regulators after China ramped up its battle against copyright infringement.

The move left millions of Chinese users disappointed after they checked out their favorite BitTorrent (BT) websites.

BT sites offer peer-to-peer file sharing protocol used to distribute large amounts of data. Last week, many such sites were either gone completely or carrying messages advising that links to downloadable movies and TV shows were unavailable.

BTChina, a popular video sharing website, displayed a notice saying the State Administration of Radio, Film and Television (SARFT) had ordered it to close because it had no license to provide audio and video content.

UUbird.com, a similar site, had a message that said it would delete all links for downloading TV series and films by mid-February "to comply with the State's laws and regulations".

Liu Pei, a 27-year-old IT engineer who visits BTChina most nights to get a free movie, was upset by the change.

"It was so popular and I can't believe it has disappeared from my life overnight," he said.

Some 800,000 users visited BTChina each day, according to statistics from http://alexa.cn.

BTChina founder Huang Xiwei said yesterday in an online statement that the Ministry of Information Industry (MII) had also revoked the company's registration number.

But he denied rumors he had been detained by the police.

The highly visible crackdown is the most recent move in the government's harder line against copyright infringement.

By the end of November, the authorities had shut 414 video and audio websites in 2009 for either operating without a license, containing pornography or other "harmful" content as well as copyright violations.