China says its first home-built aircraft carrier has completed five days of sea trials, putting it closer to joining its sister carrier in the country's increasingly powerful fleet.

The still-unnamed ship completed all assigned tasks before returning to its construction yard in the northern port of Dalian, state media reported.

The 50,000-ton carrier is China's second and is due to be commissioned before 2020 following the arrival of its air complement.

China's first aircraft carrier, the Liaoning, was bought as a mostly empty hull from Ukraine and was commissioned in 2012 along with its flight wing of Chinese J-15 fighter jets.

Both carriers are based on the former Soviet Union's Kuznetsov class design, with a ski jump-style deck for takeoff and a conventional oil-fueled steam turbine power plant.

China is seen as striving to overtake the U.S. as the dominant naval power in Asia and already boasts the world's largest navy in numbers of vessels.

Beijing says aircraft carriers are needed to protect its coastline and trade routes, but they are also seen as backing up Beijing's claims to self-governing Taiwan and virtually the entire South China Sea.