China says its homebuilt J-20 stealth fighter has conducted sea training for the first time.

Air force spokesman Senior Col. Shen Jinke posted to the service's microblog on Wednesday that the recent mission took the plane or planes out to sea for training under "actual war conditions," in a further upgrade of the force's combat capabilities.

China said in February that the plane had obtained initial operational capability and was being introduced into combat units.

First flown in 2011, the J-20 is China's answer to fifth-generation jets such as the U.S. F-22 and F-35.

With its stealth abilities, speed and maneuverability, it potentially represents a major upgrade to China's air force capabilities, although questions have been raised about some of its technologies, especially its engines.