By Agence France-Presse
The ship was "transferred from dry dock into the water at a launch ceremony" in the northeastern port of Dalian, according to the official Xinhua news agency.
It is the country's second carrier. The first, the Liaoning, is a secondhand Soviet ship built more than 25 years ago. The vessel was commissioned by China's navy in 2012 after extensive refits.
China's defence ministry has previously said that the new carrier would displace 50,000 tonnes and use conventional rather than nuclear propulsion.
It is also expected to carry China's indigenous J-15 aircraft, along with other planes.
"The launch of the new aircraft carrier is primarily a symbolic event because it will take about two years for the vessel to be equipped and to make its first real tests overboard," according to Juliette Genevaz, China researcher at the France-based Military School Strategic Research Institute.
The announcement is part of China's efforts to build a blue water navy capable of projecting power.
The Liaoning conducted its first live fire drill in December before heading to the South China Sea, raising concerns in Taiwan and neighbouring countries, such as Japan and Vietnam, who have overlapping territorial claims with China in the East and South China Sea.