China and Laos have established a jointly run training centre at a newly built airfield at Ban Keun, about 50 kilometres north of Laos's capital, Vientiane.
The two countries say the facility will be used to train pilots for Laos's air force.
So what have China and Laos said about it? What do satellite images show? How have Thailand and Vietnam reacted? And what do analysts believe is going on?
Few overseas installations
The new military facility has drawn attention as China has only a few official military facilities overseas.
They include a series of installations in the South China Sea, in disputed territory claimed by China, and a base in Djibouti that China says was established to support anti-piracy and other missions.
Beijing also paid to expand the Ream Naval Base in Cambodia, and established a joint training facility there last year, but Phnom Penh says it is a sovereign facility open to all friendly nations.
Chinese warships have made extended visits to the Ream Naval Base on Cambodia's coast. (AFP: Facebook)
'Promoting regional peace and stability'
China's Ministry of National Defense said in a statement posted online that the China-Laos Joint Support and Training Centre was officially inaugurated on September 29.
"The centre, jointly maintained and operated by both sides, is aimed at helping Laos strengthen the training of its air force pilots," the statement said.
"It is not directed against any third party and contributes to enhancing practical military cooperation as well as promoting regional peace and stability."
A report by the government's Lao News Agency echoed China's statement, saying it marked a "new step in military aviation cooperation between the two countries".
Neither country provided details on staffing and equipment.
In an article on the Chinese state-run Global Times, Chinese military affairs expert Song Zhongping said it belonged entirely to Laos and was jointly operated with no independent Chinese garrison or exclusive use rights.
The Chinese and Lao governments did not respond to the ABC's requests for comment.
Jets already on site
Satellite images of Ban Keun reviewed by Reuters, taken on September 30, showed a runway about 2,000 metres long with eight aircraft and several vehicles already on site.
Analysts told Reuters the planes appeared to be Hongdu JL-8 aircraft, which both the Chinese and Lao air forces operate.
Also known as the K-8, the two-seater aircraft is extensively used for training as well as having light-attack capabilities.
Laos currently has four of the planes, according to the London-based International Institute for Strategic Studies' annual assessment of the world's militaries, Reuters reported.
Aircraft and vehicles have already been spotted at the new facility. (Reuters: Vantor)
During the Vietnam War era, Ban Keun was an airfield known as "Lima Site 44" used by Air America, an airline secretly owned by the Central Intelligence Agency, according to records shared with Reuters by Ryan Wolfson-Ford, a South-East Asia specialist at the Library of Congress.
Satellite images showed work first began on the new facility late last year and was still underway, the news agency reported.
David Vallance, a research associate with the Lowy Institute's International Security Program, said in a post on X the runway was too short for People's Liberation Army (PLA) Air Force bombers, which required about 3,000m.
Alexander Neill, an adjunct fellow at Hawaii's Pacific Forum think tank, told Reuters the airfield looked like it had been engineered to accommodate a runway extension.
Neighbours' reactions
Thailand, a US treaty ally that shares a long border with Laos, considered itself a close partner of both Laos and China, Thailand's Ministry of Defence spokesperson Rear Admiral Surasant Kongsiri told Reuters.
He said granting permission for a Chinese facility was Vientiane's sovereign right.
"Nevertheless, Thailand will continue to closely monitor developments and how the matter proceeds, particularly with regard to building mutual trust,"
he said.
Vietnam and China have strong economic and diplomatic ties but remain at loggerheads over territory in the South China Sea, with both installing military facilities in the contested Spratly Islands.
Lowy Institute South-East Asia Program director Hunter Marston said the development would be of particular concern to Hanoi.
"More than just military presence, however, Beijing's inroads in Cambodia and Laos suggest that China's political influence within and among Vietnam's neighbours has grown, which leaves Hanoi feeling isolated and with less control over its regional environment," he said.
The Vietnamese government did not respond to the ABC's request for comment.
The Associated Press reported that a Vietnamese official with knowledge of the internal discussions said Hanoi considered the facility "as a training centre primarily focused on training and humanitarian relief".
"However, Vietnam also believes that China's decision to establish a military program at this point is intended to strengthen its influence in Laos," said the official, who spoke on the condition of anonymity because they were not authorised to talk with the press.
"China's deployment of military forces in Laos would naturally place a certain degree of additional military pressure on Vietnam as well."
China's first air force base abroad?
Some observers have described the facility as an air base.
Council on Foreign Relations South-East Asia expert Joshua Kurlantzick told AFP the Ban Keun facility was the "first air force base that China has abroad".
However, others have disputed that characterisation, with Olli Pekka Suorsa, an assistant professor at Abu Dhabi's Rabdan Academy, writing in an opinion piece for The Diplomat that the runway and apron of the "innocuous airfield" are too small to support power projection.
"To support sustained power projection operations, the airfield should have truly vast aprons, numerous aircraft shelters, and large fuel and munitions 'farms', which can be seen in similar imagery from Chinese air bases across the border," he wrote.
The Global Times labelled foreign media coverage of the centre "sensationalisation".
Song Zhongping was quoted saying the facility could only be a military base if it targeted a specific direction and a specific country.
"If we truly treated it as an air base, we would have deployed a full system of combat capabilities there,"
he said.
How significant is the new facility?
Dr Marston said the development was significant because it could expand the operational range of PLA fighter jets and might reflect Beijing's growing political influence in Laos.
But he cautioned against reading too much into it.
If the runway was expanded and became capable of hosting long-range bombers, that could allow China to project military power and surge capabilities across Thailand, Cambodia, and Vietnam, he said.
That "could cause the US to reconsider hosting large multinational security exercises in Thailand", he said.
ABC/wires