China’s notorious Great Firewall Internet censorship system looks to have snared another western service, after users of Flipboard reported that the international version of the social reading app is no longer working in the country. It was originally blocked in 2011, only to become shortly after.

Update: Flipboard says it is not self-censoring its app in China — comment from the company is at the bottom of this post.

Twitter and Facebook are among the services that are blocked in China, and it’s likely that the government’s keenness to regulate access to international media —  the very reporting that Flipboard provides access to — is behind the move. But there are plenty of questions about the censoring of Flipboard, which launched in China back in March 2012.

A series of comments from Chinese Internet users — collected by Isaac Mao, a well-known Internet figure — suggest that the company may have ‘self-censored’ its international service based on requests from the Chinese government.

That could be true. Flipboard had allowed Chinese Internet users unblocked access to Twitter, and the government is known to pressure service providers to get what it wants. On the other hand, it is equally possible that authorities flipped the switch without consulting the US startup.

A Flipboard representative said, via Twitter, that it is investigating the issue. That would suggest the company wasn’t involved in making it.

China has blocked websites belonging to a number of international news agencies, including Bloomberg and New York Times — the Wall Street Journal China edition suffered a brief block this week — so censoring Flipboard closes another avenue to overseas reporting.

While Flipboard’s local language service remains, its international app provides a unique service in China and is now only available through virtual private network (VPN) software. That’s a blow to the startup in a country that has emerged as a key growth market.

Speaking after its launch in the country, CEO Mick McCue said the number of downloads in China will “easily surpass” those in the US in the near future. We haven’t heard specific China numbers from the company, but we presume it has far exceeded its target of 5 million downloads by the end of 2012.

Tweets from Flipboard users in China include:

Yet, the service had always worked fine in China, as Robert Scoble noted when visiting in April:

We’ve reached out to Flipboard for comment.

Update: Flipboard released this statement:

We have a localized edition of Flipboard that is not blocked and works great throughout China. The International edition is the one that is blocked and that, while we wish it were still functional for people traveling to China, the government doesn’t want to allow this. We are not self censoring and the international edition of Flipboard remains accessible in China via VPN.

Headline image via Thinkstock