But experts who monitor development in the South China Sea say the photos show the islands in dispute and are consistent with satellite imagery of the development that they have been monitoring for years.
Conor Cronin, a research associate at the Asia Maritime Transparency Initiative at the Center for Strategic and International Studies in Washington, said the buildings in the new images were at the same scale as the structures in the photographs his group regularly assesses from the region. The initiative monitors development in an area long been shrouded in secrecy.
What’s striking about these images, he said, is that for the first time, significant surface-level details can be seen.
“These are kind of rare shots to see publicly,” Mr. Cronin said, noting that the detailed views of the island, seen from a much closer angle than the satellite level, were insightful. “Its another indication of how well established these facilities are and kind of the capabilities they are going to have.”
The development of the Spratly Islands has ignited outrage from neighbors that also lay claim to this portion of the South China Sea. To varying degrees, the Philippines, Taiwan, Vietnam and Malaysia all stake claim to parts of the area.
While tensions have eased somewhat as China negotiates an agreement with other players on a code of conduct for the region — which seems to allow economic development without resolving the underlying sovereignty disputes — the unabated pace of construction could stir fresh tensions.
Bonnie S. Glaser, a senior adviser for Asia at the Center for Strategic and International Studies, said the photos provided a unique perspective. She said she believed, particularly given the annotations on the images, that they were most likely taken by a military aircraft.
“What is really quite stunning is how clear you can see in these aerial photos how much has been built,” Ms. Glaser said. “It’s really up close and personal.”
A recent assessment from the Asia Maritime Transparency Initiative of satellite imagery revealed that China had developed 72 acres, both above and below ground, in the South China Sea in 2017 alone. Since the construction first began in 2013, China has developed more than 3,200 acres across the area.
More recently, the Chinese have turned their attention from dredging and reclaiming land to building airstrips, radar and communications facilities and hangars.
On Mischief Reef, which was once largely underwater, 1,379 acres have been developed by China. The latest images from the island purportedly show a nearly two-mile runway and concrete building. Analysts say it is only a matter of time before Chinese military planes begin landing there.