9 incredibly popular websites that are still blocked in China

It's the quintessential on-again, off-again relationship: Analysts believe the first time Google was blocked in the mainland was in 2002.

When the company agreed to China's censorship rules in 2006, a Chinese version was launched but issues quickly emerged between the two players.

It's not just Google search that's blocked. Gmail, Google Maps, Google Drive, Google Cloud, Google Plus and Google Photos are included in the long list of Google-related sites that are inaccessible.

"Network Timeout. The server at youtube.com is taking too long to respond" is the message users receive if they try to access YouTube in China.

The first time the video-sharing Web site was blocked was in 2008 during riots in Tibet.

"China is not afraid of the Internet," Foreign Ministry spokesman Qin Gang was quoted saying. "We manage the Internet according to law ... to prevent the spread of harmful information."

In 2007, users became unable to views pictures on Yahoo's photo sharing site. Access was restored for awhile, but then was blocked again in 2014. A test shows it remains blocked to this day. It is not known why Flickr was blocked in the first place but speculation deems the Chinese government is not a big supporter of photos being shared of uprisings.

In 2009, after deadly riots broke out in Xinjiang, Facebook users noticed they could no longer access the site.

"How can you connect the whole world if you leave out a billion people?" Facebook CEO Mark Zuckerberg said to a Stanford University audience in 2010.

Zuckerberg is amping up efforts to make China his friend though. He delivered a 30-minute speech in Mandarin to students during a 2014 visit and released a Chinese New Year video in 2015.

The Facebook-owned photo sharing network was blocked in 2014 during the widespread protests in Hong Kong. It's rumored that access may be restored in some parts, but sometimes images won't load. GreatFire, a website that tracks the firewall in China, lists it as 92 percent blocked still.

Twitter has been blocked in China since February 2011. In its place, China's own version of Twitter, Weibo, has skyrocketed to become one of China's most used apps.

Bloomberg has been blocked in China since 2012 after it published a story about the wealth of Vice President Xi Jinping's extended family. The business and financial news site remains blocked to this day along with other news sites like Reuters and the Wall Street Journal.

Dropbox has been blocked in China almost continuously since 2010, except for a short four-month access period in 2014.

One of China's main reasons for blocking websites, including Google, is because they show pornography. It's no surprise then that PornHub, the 66th most popular site in the world according to Alexa, is also blocked in the country.