WhatsApp has been blocked in China while other communication platforms like WeChat have been disrupted, as the country’s Communist Party Congress began on Wednesday.

CNBC confirmed the blockage with two producers in Beijing, who said they could not send or receive messages on Facebook-owned WhatsApp. They were also unable to change their profile picture on WeChat, the messaging service owned by Chinese internet giant Tencent, that boasts 963 million monthly users.

WeChat users received the following error message: “Due to system maintenance reasons, from today on until the end of this month, changing profile pictures, changing alias, or changing personal description line is not allowed temporarily.”

CNBC has contacted both Tencent and WhatsApp for comment and further details. The U.K.’s Chinese embassy wasn’t immediately available for comment when contacted by CNBC.

WhatsApp’s service has been on and off in China for the past week.

Users are also reporting that their virtual private network (VPN) apps are also being disrupted. VPNs are a way for people to circumvent China’s rigorous censorship method, known as the “Great Firewall”.

China has been cracking down on VPNs in the last few months. Apple pulled a number of VPNs from its App Store to comply with new regulations. And the government has ordered three major telecoms firms — China Mobile, China Unicom and China Telecom — to block access to VPNs.

This would effectively tighten the government’s grip over the internet in the world’s second-largest economy.

One CNBC producer reported problems with a VPN called Astrill. There is no media contact address for Astrill listed on its website, but a representative on an online support chat, said it is not aware of any problems related to blocking from China.

The communications crackdown comes as China’s Communist Party Congress, a once-every-five-years meeting, gets underway. It’s expected to mark a further power consolidation for President Xi Jinping.

Communications platforms are often disrupted during major government events as a way to crack down on dissent online.