Appearing to be an effort by Chinese government to curb any controversy on well before the 20th anniversary of Tiananmen massacre on June 4th it has blocked Twitter and access to other social media and blog sites including Flickr, Bing, Live.com, Hotmail.com, Wordpress, YouTube and Blogger.  However in order to evade block, if you are in China you can seek information from a good number of websites here and there online.

You can still access sites if you are in china using these two stuff here: Hotspot Shield and HideMyAss (Proxy site)