The Chinese military is busy at Lop Nur.

Hidden on the fringes of the Gobi Desert, the secretive military base is a hub for the latest and most advanced military technology that Beijing doesn’t want anyone to see.

Previously the location of China’s first nuclear test in 1964, the sprawling base in a remote part of north-western Xinjiang province now hosts the world’s longest runway, an expanding nuclear test site as well as dozens of nondescript buildings that have left leading defence experts stumped.

Isolated and tightly controlled, Lop Nur is often likened by defence experts to Area 51, the fabled compound where the US tests its most classified and cutting-edge aircraft.

Similar to Area 51, flying over the top-secret Chinese base is strictly prohibited. Yet exclusive satellite images have offered a rare glimpse into what the world’s fastest-growing military is developing and how this new technology could be used in the future.

The expansion of the base points to China positioning itself as a global superpower, with the images painting a picture of urgent drive to develop new weapons and test them secretly.

Beijing’s military is growing exponentially, with more troops, warships and fighter jets than any other military – including the US – but China is highly secretive and its armed forces lack any real battlefield experience.

Instead, China relies on expansive bases like Lop Nur to simulate conflict scenarios far from prying eyes. It means the West is not able to reliably track their rate of expansion and military technological improvements.

In recent satellite images taken by Planet Labs and shared with the Telegraph, two new, tailless stealth fighter jets were spotted on Lop Nur’s massive three-mile-long airstrip.

The long runway is believed to have been built to accommodate an experimental, reusable space plane, which was first spotted in 2020 and compared to the United States’s X-37B uncrewed spaceplane. A spaceplane is a vehicle that can fly and glide as an aircraft in Earth’s atmosphere and also function as a spacecraft in outer space.

The main apron – the portion of the airport where aircraft are parked – has been expanded, and several new hangars have been erected.

The larger of the two jets, known as the J-36, is a three-engine, two-seater fighter with no tail, which appears to have a design “optimised for stealth”, said Peter Layton, an aviation and defence expert and a visiting fellow at Griffith University in Australia.

Mr Layton explained that a key characteristic of stealth fighters is their ability to obscure radar pulses and remain undetected. “By taking the tail away, then you have a nice, smooth aircraft where the radar signals are scattered, rather than then sent back to the receiver,” said Mr Layton.

While the J-36 made its maiden voyage in December 2024, this is the first time it has been spotted at Lop Nur, which is in the Taklamakan Desert and close to the Gobi.

The large size of the aircraft, with a 65ft wingspan and 62ft in length, also suggests that it was built to carry a significant payload.

It could carry either air-to-ground weapons or long-range air-to-air missiles, said Mr Layton.

US intelligence has suggested that the design of the J-36 could also allow it to coordinate drones in a swarming attack, a tactic that China has been eager to develop.

The aircraft’s third engine – a very rare feature, especially in military aircraft – indicates that the J-36 has the ability to cruise at supersonic speed without using an afterburner, meaning it could fly at a high speed for a longer period.

The second stealth fighter, known as the J-XDS or J-50, is slightly smaller with only two engines and one seat.

Similar to the J-36, it appears to be a high-speed, high-altitude stealth fighter with low manoeuvrability designed to “launch missiles before anybody picks it up”, Mr Layton said.

“There’s an assumption that the J-36 and the [J-50] will both work together as a strike package and penetrate defended airspace at supersonic speed because they can do supersonic cruise,” said Mr Layton.

This could be strategically useful in the event of a Chinese offensive against Taiwan where the two stealth fighters could approach the island very quickly, leaving Taipei with less time to mount a defence, he added.

China claims Taiwan as its own – the government in Taipei rejects the assertion – and has made clear that efforts to build up defence capabilities are geared towards an inevitable “reunification”.

The jets, whose presence at Lop Nur were first reported by defence outlet The War Zone, are the latest in a steady stream of advanced, tightly guarded activity that has been seen at Lop Nur in recent years.

Ankit Panda, a senior fellow at the Carnegie Endowment for International Peace, and Douglas Barrie, an aerospace specialist at the International Institute for Strategic Studies, have likened the facility to Area 51.

But in China, there is evidence of a new and improved nuclear testing site.

Renny Babiarz, a former analyst at the National Geospatial-Intelligence Agency, a branch of the US Department of Defence, discovered that from 2020 to 2024, China developed a new test area to the east of the original site.

Satellite images analysed by Mr Babiarz uncovered new boreholes and horizontal tunnels, which are used to explode nuclear devices, as well as new access roads, support buildings and what appear to be storage facilities for highly explosive materials.

Mr Babiarz, now the vice-president of analysis and operations at AllSource Analysis, said that his findings strongly suggest that, after 30 years, China is preparing to carry out nuclear tests again – and it may have already started.

While there has been no seismic evidence of any large yield testing, Mr Babiarz says it is possible that China has carried out “very low yield testing” at one of the horizontal tunnels at Lop Nur.

Horizontal tunnels, which are excavated into the side of elevated terrain, are typically used for lower yield tests, whereas vertical shafts, which are drilled miles into the ground can be used for higher yield tests.

Mr Babiarz said that since his research was published he has noticed a steady stream of vehicles coming and going to one of the two new borehole sites, as well as additional construction at one of the nearby support areas.

“China has prepared to be able to test, should it want to, almost any time it wants to,” said Mr Babiarz.

“China’s done a lot of that preparation and these observations reinforce the idea that this is a new area and it’s active,” he added.

Over the same period, between 2020 and 2024, China developed three new missile silo fields, including the Hami field, located next to Lop Nur, which are used to store or launch missiles, according to a report by the Bulletin of Atomic Scientists.

China has a stockpile of approximately 600 nuclear warheads, according to the same report.

While only a fraction of what the US and Russia have produced, China is growing its nuclear weapon stockpile at a faster rate than any other country.

A new report from CNN also found that of 99 sites linked to missile manufacturing, 65 facilities had been expanded in the past five years, likely as part of a strategy to deter any US involvement if Beijing were to invade Taiwan.

US president Donald Trump announced in October that the US would also restart nuclear testing, which many interpreted as a pointed message to China as well as Russia.

Despite China’s growing capacity, the only country certain to have carried out explosive nuclear testing in the last 25 years is North Korea.