HONG KONG — The Chinese government swiftly blocked access Friday morning to the English-language and Chinese-language Web sites of The New York Times from computers in mainland China in response to an article in both languages describing wealth accumulated by the family of the country’s prime minister.

The authorities were also blocking attempts to mention The Times or the prime minister, Wen Jiabao, in posts on Sina Weibo, an extremely popular mini-blogging service in China that resembles Twitter.

The Foreign Ministry spokesman on duty in Beijing early Friday morning did not answer phone calls seeking comment.

China maintains the world’s most extensive and sophisticated system for Internet censorship, employing tens of thousands of people to monitor what is said, delete entries that contravene the country’s extensive and unpublished regulations and even write new entries that are favorable to the government.