China and Russia conducted a joint air patrol on Tuesday over the Sea of Japan and East China Sea for a sixth time since 2019, coinciding with an increase in military manoeuvres and drills by the United States and its allies in the Asia-Pacific.

The patrol is part of the two militaries' annual cooperation plan, China's defence ministry said in a statement on Tuesday.

In China's last joint aerial patrol with Russia in November, South Korea scrambled fighter jets after Chinese H-6K bombers and Russian TU-95 bombers and SU-35 fighter jets entered its Air Defence Identification Zone (KADIZ).

Japan also scrambled jets after Chinese bombers and two Russian drones flew into the Sea of Japan.

An air defence zone is an area where countries demand that foreign aircraft take special steps to identify themselves. Unlike a country's airspace - the air above its territory and territorial waters - there are no international rules governing air defence zones.

In the May 2022 patrols, Chinese and Russian warplanes neared Japan's airspace as Tokyo hosted a Quad summit with the leaders of the United States, India and Australia, alarming Japan even though China said the flights were not directed at third parties.

China's increasing military assertiveness in the region has raised concern among its neighbours as well as their Western allies such as the United States. Since last week, the coast guard of the United States, Japan and the Philippines have held their first trilateral naval exercise in the South China Sea.

Over the weekend, a Chinese warship came within 150 yards (137 metres) of a U.S. destroyer while the U.S. and Canadian navies were conducting a joint exercise in the sensitive Taiwan Strait, prompting complaints about the safety of the manoeuvre.

Shortly before that, a video showed a Chinese fighter jet passing in front of a U.S. plane's nose with the cockpit of the RC-135 shaking in the turbulence caused by the flight.