Microsoft's Bing search enginehas been blocked in China as tensions between Beijing and Washington escalate.
Attempts to open cn.bing.com has resulted in an error message for users since Wednesday.
"We've confirmed that Bing is currently inaccessible in China and are engaged to determine next steps," a Microsoft spokesperson said in a brief statement, hours after saying the company was investigating the matter.
China's Communist authorities operate an online censorship apparatus known as the "Great Firewall", which blocks a slew of websites including Facebook, Twitter and several foreign media outlets.
It was not clear whether or not Bing had joined the list of prohibited websites, or if its China service was experiencing technical difficulties.
The wording of the US company's statement "means Microsoft received no government order, but China has the power to block a URL and that may be what happened," said independent US tech analyst Rob Enderle of Enderle Group.
"China has been aggressive in terms of controlling the media, 'censorship' is kind of their middle name. If there were searches going on providing results the Chinese government didn't like, it wouldn't surprise me if they blocked the site," Enderle said.
But the analyst said it could also be a "hack gone wrong".
China's cyberspace administration did not immediately return a request for comment.
China's Great Firewall can be circumvented by using a virtual private network (VPN), which can hide a user's IP address. In 2017, Apple removed some apps that would allow internet users to use VPNs in China after Beijing issued new regulations to crackdown on the services.
While its rival Google shut down its search engine in China in 2010 after rows over censorship and hacking, Bing has continued to operate in the country along with Microsoft-owned Skype.
On Weibo, China's Twitter-like social media site, people complained about the lack of access, with some speculating that Bing too had been "walled off".
Others aired their dissatisfaction about having to use Baidu, China's largest domestic search service.
"Even Bing requires a VPN now, how exhausting," wrote one user.
"Our country is amazing, even the obedient Bing has been walled off, while Baidu flourishes," said another. "Thank you wise party leaders!"
China has tightened policing of the internet in recent years, shuttering 26,000 "illegal" websites in 2018 alone and deleting six million online posts containing vulgar content, the official Xinhua news agency said earlier this month.
Facebook's messaging service WhatsApp, which has over 1bn users globally, was blocked by Chinese authorities in 2017.
Bing complies with Chinese censorship rules, but its link to US tech giant Microsoft might have put it in the government's crosshairs as Beijing and Washington spar over trade and tech issues.
However, Bing has come under some scrutiny after an investigation by online safety company AntiToxin found that some images of child pornography would come up in search results. Microsoft called the results "unacceptable" and has since removed the illegal images.
Tsui also noted that there is growing concern over China's slowing economy, and that June will see the highly sensitive 30th anniversary of the violent suppression of democracy protests in Tiananmen in 1989.
"Beijing needs to look like they are in charge and in power," he said.
China's censorship measures are known to hide information around domestic affairs from its citizens too.
Numerous "censorship factories" are operated in the country, where thousands of citizens are paid to erase sensitive information from the internet, such as the occurrence of the Tiananmen Square crackdown.
The United States and China are locked in a bruising trade war, with US accusations that China steals technological know-how among the core disagreements.
Washington has also led efforts to blacklist Chinese telecoms giant Huawei internationally over security concerns, and one of the company's top executives, Meng Wanzhou, was arrested in Canada last month over fraud allegations on a US request.
The two sides are scheduled for new trade negotiations next week.