China on Thursday joined in global condemnation of an Islamist attack on French magazine Charlie Hebdo that left 12 people dead, describing terrorism as "a common enemy of all mankind".

The magazine's editor and some of France's most treasured cartoonists were among those killed when masked men armed with Kalashnikov automatic rifles stormed the satirical weekly's Paris offices on Wednesday.

"Terrorism is a common enemy of all mankind and a common threat to the entire international community," President Xi Jingping said in remarks carried by state news agency Xinhua.

Xi sent a message of condolences to his French counterpart, Francois Hollande, saying that China "stands ready to work with France and other countries... to safeguard world peace and protect the people of all countries," the report said.

Wednesday's massacre triggered demonstrations of solidarity around the world, with hundreds of thousands of people taking to the streets from Moscow to Washington under the banner "I am Charlie" in support of press freedom.

Beijing strictly controls the media and has recently launched one of its biggest campaigns to silence critics in years, detaining and jailing dozens of human rights activists, lawyers, academics and journalists.

China has also been engaged in a heavy handed crackdown on unrest in Xinjiang province, a vast area bordering Central Asia, which has been the scene of bloody clashes that authorities classify as religious-inspired terrorism.