Pornography websites and other pages that were previously blocked by China's internet censors were accessible inside the country today, although reasons for the change were unclear.

Beijing encourages internet use for business and education but tries to block material deemed subversive or pornographic and operates an extensive system of monitoring and censorship.

The government has launched repeated crackdowns against online pornography, calling it unhealthy and harmful.

But many Chinese-language porn sites and some foreign language sites were accessible Friday and reports said they were apparently unblocked earlier this week. Other previously blocked sites available included video-sharing site Vimeo and URL shortening site bit.ly.

It is not known if there has been a change in policy or if it was a technical issue on the part of government censors.

China's population of internet users numbers more than 400 million, by far the world's largest.