The Chinese government appears to have launched a major new internet crackdown, blocking the country’s citizens from accessing The Intercept’s website and those of at least seven other Western news organizations.

On Friday, people in China began reporting that they could not access the websites of The Intercept, The Guardian, the Washington Post, HuffPost, NBC News, the Christian Science Monitor, the Toronto Star, and Breitbart News.

It is unclear exactly when the censorship came into effect or the reasons for it. But Tuesday marked the 30th anniversary of the Tiananmen Square massacre, and Chinese authorities have reportedly increased levels of online censorship to coincide with the event.

Charlie Smith, co-founder of GreatFire.org, an organization that monitors Chinese government internet censorship, said that the apparent crackdown on Western news sites represented a significant new development and described it as a “censorship Black Friday.”

“This frenzied activity could indicate that the authorities are accelerating their push to sever the link between Chinese citizens and any news source that falls outside of the influence of The Party,” said Smith, referencing the ruling Communist Party regime.

For years, China has blocked several Western news organizations after they have published stories that reflect negatively on the government. The New York Times, Bloomberg, the Wall Street Journal, and Reuters have all previously been censored, rendering their websites inaccessible in the country.

China operates an internet censorship system known as the Great Firewall, which uses filtering equipment to stop people in the country from accessing content published on banned websites that are operated outside China’s borders.

It is possible to circumvent the censorship using tools such as a virtual private network, or VPN. However, use of technology that bypasses the Great Firewall is banned — and people in the country who sell access to these services have been jailed.