Access to the website of the Guardian newspaper has been blocked in China, according to censorship-tracking website greatfire.org.
The Guardian stated that "numerous attempts to access the site from multiple browsers, devices and locations across Beijing all failed without the aid of firewall-circumventing software."
The Guardian is the latest in a line of media outlets that have been blocked in China.
"The reasons for the Guardian block are unclear - no China-related stories published by the Guardian in the past two days would obviously be perceived as dangerous by the country's leadership," the newspaper said in an article on its guardian.co.uk website.
When the paper made inquiries, a China Foreign Ministry spokeswoman said: "This is the first time I have heard of this. I don't understand the situation. You can inquire with China's relevant department."
The Guardian ran a report on 6 January about the tension in China's ethnically diverse and troubled northwestern region of Xinjiang and the United States expressed concern about China's efforts to restrict the activity of foreign news organisations.
However, the Guardian said it "has covered the subject before without any noticeable fallout".
China has already blocked the New York Times and Bloomberg News websites for more than a year after the news heavyweights published reports about the wealth of family members of former Premier Wen Jiabao and President Xi Jinping, respectively.
Elsewhere, Thomson Reuters and the Wall Street Journal's Chinese-language websites were blocked in mid-November, although both became accessible on Christmas day.