Some popular social apps have reported service outages of unconfirmed cause in mainland China on Thursday, two days after a huge pro-democracy protest was held in Hong Kong.

Users of Line and KakaoTalk in China have noticed disruption on some features of the mobile messaging apps beginning Tuesday. Yahoo Inc's photo-sharing app Flickr also experienced an outage on the same day, according to The Wall Street Journal.

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The outage started on the eve of July 1, when Hong Kong protesters began staging a pro-democracy rally, giving rise to speculations that the Chinese government was behind the service limitations. China often blocks international websites and mobile app services during sensitive situations.

A Line spokeswoman said they did not know when the service would resume its availability in mainland China. Kakao Corp, on the other hand, said via spokeswoman Sonia Im that their app's users could still access some of the platform's features but could not add new friends.

China-based Line users could get notifications about an incoming message, but the message itself could not be accessed. The KakaoTalk app could be downloaded but the mobile phone users could not register in the service.

The Line app, which is very popular in Hong Kong, could have been easily used by residents to share updates on the pro-democracy rally.

References to the Hong Kong demonstrations have been more strictly blocked on local social media compared to that of the Tiananmen Square anniversary, according to censorship tracking service WeiboScope.

Meanwhile, several Google Inc services are still inaccessible by users in mainland China since being blocked last month. Analysts say this is part of China's attempt to maintain a firm grip on the flow of information via the Internet and limit the influence of foreign companies on its citizens.

Since Xi Jinping became president in 2012, he has employed several steps to give the government more control over the Internet. His regime has formed a new committee to monitors cybersecurity and has launched an anti-pornography campaign.

Facebook's WhatsApp, Tencent's WeChat, Rakuten's Viber, and other popular messaging apps received no reports of service disruption.