Bing is down in China, several users have reported, stoking fear that Microsoft’s search engine might be the latest service to get blocked by the local government’s Great Firewall. Microsoft says it is investigating the matter.

“We’re aware of reports that Bing may be inaccessible to some customers in China and are investigating,” a Microsoft spokesperson told VentureBeat. Reports from local users about their inability to access Bing started pouring in late Wednesday (local time).

Bing blocked in China? pic.twitter.com/GpOG1eMmSr — Shen Lu 沈璐 (@shenlulushen) January 23, 2019

WebSitePulse, an online service that tracks outages in China, confirmed that cn.bing.com — the web address for Bing in China — was inaccessible in several parts of the country.

While the cause of the outage remains unknown, it comes a day after Baidu, the most popular search engine in China, received complaints that it was promoting low-quality articles from Baijiahao, a news organization it owns, and other properties, in its search engine. Baidu said on Wednesday that it would improve its media aggregating service.

The Great Firewall is a state-run internet censorship system, which the local government has used to block several global services, including Google and Facebook.

Microsoft made Bing available in China in June 2009. The company pronounces Bing as “biying“ in the nation, which means “must respond or answer” in Chinese. Bing has received its fair share of criticism from local users, as it censors some results, in accordance with the local laws.

In recent years, Bing has further skewed its service to prefer news results from state-run media outlets Xinhua and China Daily, according to reports. The search engine, which rivals Baidu’s offering, Shenma, Sogou, and Yahoo in China, attracts north of 220 million page views each month, according to web analytics service SimilarWeb.

Update at 6:15 p.m. Pacific: Microsoft has confirmed that Bing has been blocked in China. “We’ve confirmed that Bing is currently inaccessible in China and are engaged to determine next steps,” a Microsoft spokesperson told VentureBeat.

Update at 1:17 p.m. Pacific on January 24: Bing is accessible in China again. In a statement, a Microsoft spokesperson said, “We can confirm that Bing was inaccessible in China, but service is now restored.”

Microsoft did not offer an explanation for Bing’s outage, but in a televised interview with Fox News at the World Economic Forum, company president Brad Smith addressed the matter. He noted that this is not the first time Bing has faced an outage in China. “It happens periodically.”

He added, “You know, we operate in China pursuant to some global principles that’s called the Global Network Initiative in terms of how we manage censorship demands and the like. There are times when there are disagreements, there are times when there are difficult negotiations with the Chinese government, and we’re still waiting to find out what this situation is about.”