China's next South China Sea military base takes shape on Antelope Reef

"If Fiery Cross is the guide, I'd expect the runway paved in the first half of 2027 and a first landing by mid-2027, possibly earlier," said Ben Lewis, founder of the open-source data platform PLATracker, referring to a three-kilometre runway built on a reef in the disputed Spratly Islands further south in 2015.

"They've had 10 years to get faster at this," he said.

Lewis said he had yet to note signs of excavation for possible ammunition and fuel storage, which a base of this scale would need.

China's defence ministry did not immediately respond to a Reuters request ​for comment.

China has yet to acknowledge construction of a new military base, while state media have said Antelope will serve civilian needs such as weather forecasting and maritime and scientific research.