China is blocking access to Google's popular Gmail service, according to data from Google and analysis from Dyn Research.

Traffic has dropped to nearly zero, per Google's transparency reports, which provides real-time information about usage of its services.

Dyn Research, an Internet analysis firm, said it confirmed that an "IP-level" block of Gmail had occurred.

"China has a number of ways they can block content. One of the crudest ways is to just block an IP address, and when you do that, you block all the content available at the IP," Earl Zmijewski, Dyn's vice-president of data analytics, told Mashable.

Zmijewski said that much of China's Gmail access is routed through Hong Kong IP addresses, which were being blocked. He said he checked six different locations, and found that each one was blocked.

China and Google have long had a complicated relationship. Earlier this year, the country blocked access to all Google services in June ahead of the 25th anniversary of the Tiananmen Square massacre.

Before that, China blocked Google services in 2009 and 2012. In 2010, Google publicly said it would no longer censor its search engine in China, a move that the company acknowledged could mean withdrawing from the country entirely.