Chinese internet users have lost access to Microsoft's Bing search engine, sparking complaints about the ruling Communist Party's increasingly tight online censorship.
Comments on social media accused regulators of choking off access to information.
Others complained they were forced to use Chinese search engines they say deliver poor results.
"Why can't we choose what we want to use?" said a comment on the Sina Weibo microblog service.
Bing complied with government censorship rules by excluding foreign websites that are blocked by Chinese filters from search results.
But President Xi Jinping's government has steadily tightened control over online activity.
Microsoft confirmed in a statement that Bing was inaccessible in China.
Bada bing bada boom: China appears to have blocked the Microsoft search engine pic.twitter.com/pNylXTgRX9— Anna Fifield (@annafifield) January 24, 2019
It said the company is trying to "determine next steps" but gave no details.
China has by far the biggest population of internet users, with some 800 million people online, according to government data.
The Communist Party encourages internet use for business and education but blocks access to foreign websites run by news organisations, human rights and Tibet activists and others deemed subversive.
Since coming to power in 2012, Mr Xi has promoted the notion of "internet sovereignty", or the right of Beijing and other governments to dictate what the public can do and see online.
Chinese filters block access to global social media including Twitter, Facebook and YouTube.
Officials argue such services operating beyond their control pose a threat to national security.
Mr Xi's government has also tightened controls on use of virtual private network technology that can evade its filters.
Alphabet's Google unit operated a search engine in China until 2010 that excluded blocked sites from results.
The company closed that after hacking attacks aimed at stealing Google's source code and breaking into email accounts were traced to China.
That has helped Chinese competitors such as search engine Baidu.com to flourish.
But Baidu has been hit by repeated complaints that too many search results are irrelevant or are paid advertising.
"Is it really necessary to force me to use these garbage domestic search engines?" said a comment on Sina Weibo.
- Press Association