China is blocking many sites from around the world with its program called The Great Firewall. What is the Great Firewall? According to Wikipedia.org

The Great Firewall is the combination of legislative actions and technologies enforced by the People’s Republic of China to regulate the Internet domestically. Its role in internet censorship in China is to block access to selected foreign websites and to slow down cross-border internet traffic.

https://en.wikipedia.org/wiki/Great_Firewall

You can check easily if a site is accessible from China with some online services. One such service is

http://chinafirewalltest.com

The Facebook.com site is being blocked:

china firewall test
Facebook.com blocked by Great Firewall

Other examples of services that you can use are:

https://www.comparitech.com/privacy-security-tools/blockedinchina/
https://blocky.greatfire.org/ (available in Chinese and English)