The shutdown across a nation of 80 million people in Iran was the first to effectively isolate a modern, highly developed domestic network, experts say.

Experts say freedom on the internet is at risk as more countries try to control what their citizens see and say on the worldwide web.

Washington already raised concerns last September about China's cyber security law, asking Beijing not to enforce it until it addressed the risk of it disrupting cross-borders information transfers.

Searches for the Chinese words "Jin San Pang" on the search engine Baidu and microblogging platform Weibo returned no results this week.

Chinese controls on information have tightened and loosened over the years, but some say this is China's most severe crackdown in decades on how people learn about the world around them, talk to each other and do business.

China is blocking VPN services that let users skirt online censorship of popular websites such as Google and Facebook amid a wider crackdown on online information, tech companies and specialists said Friday.

Alibaba shook up China's vast but sleepy retailing industry by popularizing online shopping. Now it and China's other Internet companies are mounting challenges in areas from banking to broadcasting.