Internet users in China were unable to open the main site of Google, the world's biggest search engine, late on Wednesday evening, and the company said it was investigating.
Users in Shanghai and Beijing said they got an error message when they tried to reach the U.S. company's main search page (www.google.com), its Chinese search page (www.google.com.cn) and mail service (www.gmail.com) between around 10pm and 11pm local time.
It was not clear how widespread the blockage was.
A company spokeswoman at Google in the U.S. said the firm was checking reports of problems with access in China. Most users appeared to get access again by 11 p.m.
The disruption came less than a week after China's Internet watchdog ordered Google to stop overseas websites with pornographic and vulgar content from being accessed through its Chinese-language search engine.
There was no mention of the blockage on Xinhua news agency or any other official Chinese news services.
Foreign Internet firms are keen to do business in the world's largest online market, but many western companies have been accused by critics of bowing to Beijing's demands for censorship in their bid to carve a niche in the China market.
The Chinese government recently ordered all new personal computers to carry Green Dam filtering software designed to block pornographic Internet content from July 1, leading to fears China was using its campaign to protect children from unhealthy content as a way of tightening censorship.
(Reporting by Chris Buckley and Emma Graham-Harrison in Beijing, Lucy Hornby in Shanghai, George Chen in Hong Kong and Alexei Oreskovic in San Francisco; editing by Philippa Fletcher)