By Tessa WongAsia Digital Reporter, BBC News

They were trusted and favoured by Xi Jinping. Now, they seem to be vanishing.

In recent months, the disappearances of several high-ranking Chinese officials have sparked intense speculation over whether Mr Xi is embarking on a purge, particularly of those linked to the military.

The latest person who appears to have fallen from grace is defence minister Li Shangfu, who has not been seen in public for some weeks now.

While his absence was not seen as unusual at first, scrutiny intensified when a top US diplomat pointed it out. A Reuters report later said General Li, who used to oversee arms procurement for the People's Liberation Army (PLA), was being investigated over military equipment purchases.

His "disappearance" comes weeks after two top officials in the Rocket Forces - the military arm that controls nuclear missiles - and a military court judge were removed.

Fresh rumours are now circulating that some cadres in the Chinese Communist Party's (CCP) central military commission that controls the armed forces are also being investigated.

Little to no official explanation has been given for these removals, apart from "health reasons". In this void, speculation has blossomed.

The main theory is that authorities are cracking down on corruption in the PLA.

The military has been on heightened alert - in July it issued an unusual call-out asking the public for tip-offs on corruption in the past five years. Mr Xi also launched a fresh round of inspections, criss-crossing the country to make five visits to military bases since April, according to checks by BBC Monitoring.

Corruption has long been a problem in the military particularly since China began liberalising its economy in the 1970s, noted James Char, a research fellow at Singapore's Nanyang Technological University who studies the relationship between the CCP and the military.

Every year China spends more than a trillion yuan on the military with some going towards procurement transactions, which for national security reasons cannot be fully revealed. This lack of transparency is further compounded by China's one-party centralised system.

Unlike the kind of public scrutiny other countries' militaries are subjected to, China's armed forces are overseen exclusively by the CCP, pointed out Dr Char.

While Mr Xi has had some wins in tempering corruption within the armed forces and restoring its reputation to some extent, "rooting out corruption is a formidable if not impossible undertaking" as it would require "systemic redesigns which I'm afraid the authoritarian state remains averse to", Dr Char added.

"Until the CCP government is willing to put in place a proper legal system no longer sanctioned by itself, such purges will keep occurring."

But the disappearances could also be put down to a deepening paranoia in Chinese government as it navigates its tricky relationship with the US.

In July, an expanded counter-espionage law took effect in China, giving authorities greater power and reach in conducting investigations. Soon after, China's state security ministry publicly encouraged citizens to help them combat spy activities.

General Li's disappearance echoes that of foreign minister Qin Gang, whose removal in July also caused speculation to reach a fever pitch. This week, the Wall Street Journal reported Mr Qin was being investigated over an alleged extramarital affair that resulted in a child born in the US.

"Having an affair is not disqualifying in elite [Communist Party] circles, but having one with someone who may be suspected of having foreign intelligence ties and producing a child holding the passport of your key geopolitical rival, if not enemy, may now be," noted China analyst Bill Bishop.

There is also speculation that Mr Xi is acting under internal party pressure to clean out the stables, as China struggles with a slowing post-Covid economy and soaring youth unemployment. Under China's political system, Mr Xi is not only China's president but also the top leader of the military.

Viewed one way, the disappearances are a sign of instability in Mr Xi's leadership.

Observers have homed in on the fact that General Li and Mr Qin, who were not just ministers but also occupied more elevated positions as State Councillors, were favoured by Mr Xi. Their sudden downfalls could therefore be seen as a lack of judgement by the Chinese president.

If one sees the disappearances as a political purge, then the fact that he had to enact one so soon after consolidating power at the party congress last year, where he successfully neutralised potential rival factions and stacked key committees with his allies, is a bad look.

But the other view is that it is yet another show of strength by Mr Xi.

The son of a purged CCP official, Mr Xi is famous for his public crackdowns on corruption - which also act as political purges aimed at rooting out his enemies, say observers.

Since Mao Zedong, no other Chinese leader has come close in matching the scale of Mr Xi's crackdowns. They are estimated to have netted thousands of cadres over the years, and have targeted both low-level and top officials beginning with his "tigers and flies" campaign launched shortly after he took office in 2013.

He also targeted the armed forces and by 2017 had removed more than 100 senior officers. At that time state news agency Xinhua said in an article that the figure "far exceeded the number of generals killed in wars to create the new China".

But the biggest question is over the signal the latest disappearances sends, and their ultimate impact.

Observers say they would create a climate of fear in the military and government. Though this may be the intended outcome to ensure compliance, it would also have a demoralising effect.

Years of systematically rooting out those who have fallen out of his favour and packing top posts with his followers could mean that Mr Xi has surrounded himself with yes-men. The risk of groupthink is the "real instability" of Mr Xi's leadership, as it could adversely affect China's national security and foreign policy, noted Dr Char.

The disappearances in fact have happened during a tense period in the Taiwan Strait, with China sending more warships and military jets there in recent weeks.

Any disruption in communication over foreign policy and defence diplomacy would be "especially concerning" as "accidents could happen and managing escalation could become more challenging", said Ian Chong, a non-resident fellow at the Carnegie China think tank.

Others however argue that China's military leadership is robust enough to withstand the replacement of some top officials, and point out that it has been careful to operate below the threshold of war.

Still others believe the disappearances are unlikely to have a long-term impact on Mr Xi's leadership stability. None of the cadres who have been targeted so far are part of his inner circle, pointed out Neil Thomas, an expert in Chinese elite politics with the Asia Society Policy Institute.

What most observers can agree on is that these incidents highlight the opacity of the Chinese system. "It further sharpens questions about the continuity of policy implementation and the credibility of any working-level promises or assurances," noted Dr Chong.

Ultimately, these officials' vanishing acts have fuelled a "resulting unease".

Additional reporting by BBC Monitoring.

ncG1vNJzZmivp6x7o67CZ5qopV%2Bjsri%2FjrCmq6SUYq60tcBmmqGhnpZ6d4KXcGxuamY%3D