China's online watchdog has launched an investigation into reports of multiple violations at some of the country's largest online services, Bloomberg has reported.
According to the report, the Cyberspace Administration of China has instructed its Beijing and Guangdong branches to look into reports that news services run by Tencent, Baidu, and Weibo are carrying user-generated content laden with "violence, porn, rumors" disruptive to social order.
The investigation comes as the government continues to tighten scrutiny over internet content, the report explains.
Popular social media websites such as Facebook, Twitter, and YouTube are blocked in the country, with a pilot free-trade zone active in Shanghai in the past that allowed some access to such content, although still heavily restricted. Services including Microsoft Outlook and Gmail have also been banned under the laws.
Last month, Apple pulled VPN apps from the App Store in China.
China has long operated the world's most sophisticated online censorship mechanism, known as the Great Firewall, and the use of VPNs by residents provides a loophole which can be used to circumvent the country's surveillance and blocking lists.
At the beginning of last year, China upgraded its Great Firewall and began to crack down on the use of VPNs within the Middle Kingdom.
The revamped internet filter made it difficult to work around the Facebook ban, and called it a move aimed at fostering the "healthy development" of the internet in China.
The Chinese government in July ordered state-owned internet service providers, including China Mobile, China Unicom, and China Telecom, to completely block access to VPNs by February 2018.
It followed a 14-month campaign the Chinese Ministry of Industry and Information Technology launched in January, aimed at cracking down on "unauthorised" web platforms and services the government does not approve of.
In what the Chinese government labelled a "clean up" which will "standardise the market order" and "promote healthy and orderly development", the program forces ISPs, VPN providers, datacentres, and content delivery networks to gain a licence and approval from Chinese officials to operate.
The campaign described VPNs as "illegal cross-border business issues" that need to be controlled, and deems it illegal for businesses to operate outside of their specific licence limitations.
According to Bloomberg, China has recently applied increased pressure on internet media platforms in the run-up to an important Communist Party congress later this year.
In a bid to shutter potential sources of disruptive information, the report says the Chinese government has also shut live-streaming services and websites, tightened regulations governing internet access, and issued repeated warnings about the need to clean up content through various agencies.