The social networking site Facebook appeared to be accessible to Internet users in several parts of China Tuesday, despite its usually being blocked in the tightly controlled Communist country.

VOA's Beijing bureau was able to access Facebook early Tuesday using the prefix “HTTPS” instead of the usual “HTTP,” which is a way of accessing websites using a secure connection.

Various other Internet users posted comments on another social networking site – Twitter – on Tuesday saying they were also able to visit the site using the same method.

However, Facebook did not appear to be accessible everywhere in China, with online users reporting the usual blockage in Chongqing and Ningxia.

China boasts the world's largest online population. But the online activity of its estimated 500 million Internet users is tightly monitored and censored with an extensive online filtering system dubbed the “Great Firewall of China.”

Facebook, along with Twitter and YouTube, are all normally blocked. The government says the policy is aimed at maintaining social stability, and that it will help stop the spread of false rumors and inappropriate material.

About half of China's online population uses hugely popular local equivalents, known as weibos, which are more easily censored by government monitors.

However, many technically-savvy Internet users are often able to bypass the firewall and access foreign websites using a virtual private network, or VPN, which redirects Internet traffic through an external server and helps keeps browsing history private.