The Chinese air force completed a military drill in the airspace above the West Pacific Ocean on Thursday, crossing the Miyako Strait for the first time, a military spokesperson said on Thursday.

According to Shen Jinke, spokesman for the People's Liberation Army (PLA) Air Force, PLA aircraft flew over the West Pacific via the Miyako Strait.

The Miyako Strait is an international waterway lying between Japan's Miyako Island and Okinawa Island.

They returned to their base later the same day, having successfully completed the drill which aims to improve the PLA Air Force's mobility and combat readiness over the high seas.

Shen stressed that the drill is a routine exercise of the air force's annual training plans and is "in line with international laws and practices."

"The drill is not targeted at any country and carries no threat against other countries and regions," he said, adding that similar drills in airspace far offshore from coastlines were a common practice among countries on the coast.

It was carried out in international airspace without flying at the altitude of main civil aviation aircraft, Shen said.

He noted that none of the international flights were affected by the drill.

The spokesman said future exercises involving PLA aircraft flying across the "first island chain blockade" in the high seas will be conducted under certain circumstances and in accordance with international laws and practices.

The "first island chain" refers to the first major archipelagos off the East Asian continental mainland, including the Japanese archipelago, Ryukyu Islands, China's Taiwan and northern Philippines, according to the Xinhua News Agency.

In the 1950s, Washington came to regard the chain as an important barrier to contain China and other communist countries, and the US and its allies provided a strong military presence and advanced weapons at bases along the line, Xinhua said.

"Crossing the first island chain shows the Chinese armed forces are determined to ignore the so-called blockade by familiarizing themselves with the maritime conditions outside the chain," said Song Zhongping, a military affairs commentator.

In March, the PLA Air Force conducted its first military drill above the West Pacific Ocean, flying across the Bashi Channel south of Taiwan.

"The international airspace above the Miyako Strait is narrower than that above the Bashi Channel, which requires more precise positioning and greater expertise of pilots to avoid intruding into other countries' territorial airspace," Fu Qianshao, an air-defense expert, told the Global Times.

Fu said he expects the navy, which conducted several separate drills, and the air force to conduct joint training exercises in the high seas in order to gain more competence in combined air-sea battles.