One of the most popular video-sharing websites in China has been shut down, prompting fears the Government may be tightening its control over the internet.

The site, 56.com, which usually offers YouTube-style video, has been suspended for more than two weeks. A message on the home page blames a server upgrade, but it would be unusual for such routine maintenance to take so long.

Executives at the company refused to explain the delay, according to the Wall Street Journal, prompting concern that it may have fallen foul of regulators. 56.com is one of the three largest video-sharing sites in China, and along with similar sites has been closely scrutinised by the Government in recent months.

The site, whose name sounds similar to the Chinese for 'I'm happy', usually offers a mix of amateur video clips, as well as professional content deriving from one of its many content partnership, including one with the National Basketball Association to run footage from games.

The State Administration for Radio, Film and Television, one of the Government agencies which monitors internet video, didn't respond to requests for comment, the Wall Street Journal said, nor did the 56.com's chief financial officer. Executives at 56.com's investors, which include the venture firm Sequioa and the Disney-backed fund Steamboat Ventures, also declined to comment.

China already closely controls some aspects of the internet – including the results that search engines such as Google are able to display to Chinese users. But of late it has turned to video-sharing sites, which have increased dramatically in popularity. According to one government survey, 77 per cent of the country's 225 million internet users visited online video sites.

In December the Government issued new rules which held that in order to operate, video-sharing sites must be part state-owned. Regulators later issued guidance that some privately run sites may continue if they were given licenses and agreed to abide by content restrictions, but it has so far refused to give licenses to the three largest sites – Tudou.com, Youku.com and 56.com.

Tudou.com - which includes the US technology media and research company IDG among its backers - was shut down briefly in March, but was online again 24 hours later. Some analysts have suggested that the site has fared better with the authorities because its management has closer ties to Beijing. 56.com has been offline since June 3.

Dozens of smaller sites have also been shut down, apparently for failing to comply with content restrictions which prevent, for instance, any reference to the spiritual group, Falun Gong, and any pornography.

"Video-sharing are a mass medium in China - more than half the online population use them, so they're obviously something the Government is going to want to control," said Jeremy Goldkorn, editor of Danwei.com, a site which tracks the media and advertising industries in China. "If you run one, then Government relations is going to be a key part of the business."

Most Chinese sites employ teams who comb through content as it uploaded - unlike YouTube, which waits for offensive or inappropriate content to be pointed out by users before it is taken down.

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