Google Inc's Web search and mobile services in China were blocked on Thursday, according to a message on the company's website.
It was unclear whether access had been blocked by the Chinese government or if it was a temporary service disruption. A Google spokesman said he did not have any immediate information on the change in service availability.
Some users on the microblogging service Twitter reported no problems accessing Google on Thursday.
A dispute between China and Google over Internet censorship blew up in January when the world's largest search engine stunned markets and consumers by warning that it might quit China. At the time, Google said it would not provide the censored search results that China requires.
Tensions appeared to have cooled earlier this month when China granted Google one-year approval to keep operating its Chinese search site. Until Thursday, Google's search service appeared to be mostly accessible in China this week.
Shares of Google were down 1.4 percent after hours to $478.00, while shares of Baidu Inc, the biggest search provider in China, rose 3.5 percent to $82.00.
Access to Google's various online services have long been spotty in China. In recent months, Google has reported partial blocking of access to its search, mobile and news services on many occasions.
Since Google began providing service availability data four months ago, Thursday marked the first time Google said its search, ads and mobile services in China were fully blocked.
Google defines fully blocked as 67 percent to 100 percent accessibility disruptions on its website reporting China availability.
(Reporting by Paul Thomasch in New York and Alexei Oreskovic in San Francisco; Editing by Tim Dobbyn)