Telegram and other secure messaging apps have been used by Hong Kong protesters who want to hide their identities while coordinating protests to avoid surveillance.
China's cyberspace administration did not immediately respond to AFP's request for comment.
Communication apps such as Telegram, which use encryption to secure messages, are often used by activists to organise protests.More news: Instagram down: App restored after suffering global outage
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Mark Skilton, professor of Practice at Warwick Business School, said: "This type of attack is government censorship using cyber tools to block Internet traffic".
Britain formally controlled Hong Kong as a colonial power until it was handed over to China in 1997, but the city has enjoyed relative autonomy from mainland China's authoritarian police state. South China Morning Post reported that earlier this week Ivan Ip, a man who ran a large Telegram messaging group, was arrested by the police. Imagine that an army of lemmings just jumped the queue at McDonald's in front of you - and each is ordering a whopper.
The protests are over fears that passing an extradition bill in the country will lead to Hong Kong becoming more under the control of China.
Hong Kong protesters have grown increasingly concerned about legal repercussions as Beijing tightens its influence over the former British colony and the local government prosecutes demonstrators.
Back then, the country was also going through internal issues where the people stood up against their government, as China started cracking down on the country's human rights lawyers.