Gmail activity has flat-lined in China, raising suspicions about further government censorship of the Internet.

Gmail traffic in China tumbled to near zero on Dec. 26 and hasn't budged since, according to Google's transparency report.

Dyn Research, a group of scientists that reports on Internet issues, tweeted that the Chinese government had deliberately blocked Gmail in China, according to its analysis. The research group also said that "blocks" of Google served from Hong Kong have shut down throughout the country.

Google (GOOGL) and China have had a testy relationship since 2010, when Google pulled its business out of the country. Google's websites are no longer served in China; instead, its servers reside in Hong Kong, which is not subject to the same censorship laws that the rest of China is.

Google's move to Hong Kong forces China to actively censor or block Google content for its citizens -- something Google said it was no longer willing to do four years ago. Google search, YouTube, photos and maps have all experienced major outages and service disruptions this year, according to Google's transparency report.

This could be latest sign of China's ruling Communist Party exerting its influence on Hong Kong. In recent months, Hong Kong erupted into violent pro-democracy protests.

Related: Why North Korea's economy can't live without China

China's ruling Communist Party has for decades operated a massive censorship project called the Great Firewall of China. Social media platforms including Facebook (FB) and Twitter (TWTR) are banned, and thousands of websites cannot be accessed from inside China.

Internet stability in the region has been a bit shaky. China's neighbor North Korea lost its Internet connection and went dark on Dec. 22. It was unclear whether the country suffered a massive power outage, or got unplugged by an outside entity.

That came after the FBI accused the North Korean government of hacking Sony Pictures for revenge over its movie "The Interview," which depicts the fictional assassination of Kim Jong Un. The North Korean government denied the allegations.