The carrier, known only as "Type 001A", set out for the trials from a port in northeastern China at around 6.45 am (2245 GMT Saturday), according to state broadcaster CCTV.

Footage aired by CCTV showed the imposing ship accompanied by several smaller military craft leaving a wharf and heading out to sea under grey skies.

It is the first time the carrier's engine, propulsion and navigation systems will be tested at sea, state media said, a year after the vessel first took to the water at its official launch.

Expected to be commissioned by 2020, the ship will give China a second aircraft carrier to beef up its navy as it asserts its claims in the disputed South China Sea and seeks to deter any independence movements in Taiwan.

China's sole operational aircraft carrier, the Liaoning, is a repurposed Soviet ship bought from Ukraine, which went into service in 2012.

Neither the Liaoning or the new ship are nuclear-powered, but both can carry around 40 planes and have similar "ski jump" ramps, an old launch system that forces aircraft to carry fewer weapons in order to hold more fuel for take-off.

The possession of a homegrown aircraft carrier places China among the few military powers with such vessels, including the United States, Russia and Britain.

But it would still be no match in size or range to the nuclear-powered vessels of the United States Navy, which has 11 carriers.

However, Beijing has embarked on an extensive project to build a "blue water" navy and modernise its two million-strong military, the world's largest.

The Type 001A carrier will displace 55,000 tonnes and use conventional propulsion, according to the defence ministry.

Chinese state media have been speculating that a third home-made aircraft carrier was in the works, but the defence ministry has yet to confirm this.

China's defence budget rose 8.1 percent to 1.1 trillion yuan ($175 billion) in 2018, but it is still only about one-quarter that of the United States.