Warplanes attached to China's Eastern Theatre Command during joint exercises around Taiwan, August 7, 2022. The Chinese military's official newspaper says the air force is operating in "previously unreachable areas." China also recently sent advanced fighter jets across the median line in the Taiwan Strait. Get a daily selection of our top stories based on your reading preferences

The People's Liberation Army has said it had expanded its air control to "previously unreachable" areas before the recent Taiwan Strait crisis.

Its most advanced J-20 fighters have repeatedly been scrambled to "check and identify foreign military aircraft entering our East China Sea Air Defence Identification Zone," most recently in late July, the official newspaper PLA Daily reported on Wednesday.

J-20s also took part in the recent mass crossings of the median line in the Taiwan Strait in the wake of US House Speaker Nancy Pelosi's visit to the island earlier this month.

Following last week's exercise, the PLA said it would "keep a close eye on the changing situation … and organise combat and surveillance patrols in the direction of the Taiwan Strait in a regular manner," which was interpreted as an announcement that the PLA would establish a "new normal" presence beyond its previous range and effectively wipe out the median line.

In addition to circling Taiwan, the air force has also established an air defence identification zone (ADIZ) in the East China Sea, conducts regular patrols over the South China Sea, held training exercises over the Pacific and with their Russian counterparts, the PLA Daily article said.

The article said the air force was now "flying the routes that had not been flown and accessing the airspace that had never been reached" as it became capable of carrying out "both defensive and offensive operations."

The origins of its transformation came in a 2004 defence white paper that called for the air force to move beyond "homeland defence," followed by massive investment and modernisation.

The creation of the East China Sea air defence identification zone in 2013 and eventual control was also a key part of this transformation.

"When we first started our patrols, there were protests from some countries and provocations by foreign military aircraft," J-20 pilot Yang Chunlei told PLA Daily.

"Since our air and sea forces turned the management of the East China Sea ADIZ into a routine, aircraft from most countries now basically fly in accordance with our protocols."

An air defence identification zone is a unilaterally declared area, in which the claimant country tracks and identifies aircraft flying within that space to protect national security.

Normally the air force requires aircraft to identify themselves and respond to commands. It can also issue warnings to suspicious foreign aircraft and send fighters to track or even intercept them.

Over 20 countries have unilaterally declared ADIZs, though they are not formally recognised under international law.

In practice, they can extend far beyond the country's sovereign airspace to allow enough reaction time to deal with possible national security threats, with the US zone stretching to 400 nautical miles (740km) in places.

Mainland China's ADIZ does not exceed its claimed exclusive economic zone in the East China Sea, but the ongoing territorial disputes in the region means it overlaps with the ADIZs claimed by Japan, South Korea and Taiwan.

"The PLAAF has been through a difficult path of development, from lagging far behind, to then being slightly out of reach, to being on par with rivals now in the enlarged airspace," Song Zhongping, a former PLA instructor, said.

When Beijing announced its ADIZ in November 2013, both the US and Japan rejected it, sending their own warplanes into the area instead.

Over the years this has led to a series of incidents, including one in June 2016 when an encounter between two PLA Su-30 fighters and Japanese F-15 jets, where Beijing accused the Japanese planes of beaming their fire control radars on the Chinese planes — a possible precursor to an attack. Tokyo denied the claims.

The following year the US accused two Chinese Su-30s of carrying out some "unprofessional" manoeuvres within 45 metres of a US WC-135 nuclear spy jet.

In March this year the US Pacific Air Forces commander, Gen. Kenneth Wilsbach, said that there had been "a close encounter" between a J-20 and US F-35 over the East China Sea.

It is unlikely that the PLA will formally extend the current ADIZ to cover the Taiwan Strait, according to Antony Wong Tong, a Macau-based military commentator.

"The problem is that it would cause too huge an international impact. So, in the foreseeable future this is not happening, because there is a risk of it easily getting out of control at any time and it is not necessarily in Beijing's interests," said Wong.