The construction on Fiery Cross Reef is part of a larger Chinese reclamation project involving scores of dredgers on at least five islands in the South China Sea. China is converting tiny reefs, once barely visible above water, into islands big enough to handle military hardware, personnel and recreation facilities for workers.

Satellite images of the reclamation efforts have been released in steady doses over the last few months, as smaller countries with claims to islands in the area have voiced concern about China’s accelerated construction, and as the United States has stepped up its criticism.

During his recent first trip to Asia as the American defense secretary, Ashton B. Carter said in Japan that the reclamation efforts were seriously aggravating tensions between Beijing and Washington and hurting prospects for diplomatic solutions.

After Mr. Carter spoke, the Center for Strategic and International Studies, a Washington research group, released images of Mischief Reef, also in the Spratly archipelago, that showed large-scale dredging of sand and coral to create land mass on what had been a partly submerged reef.

The construction on Fiery Cross Reef, hundreds of miles west of Mischief Reef, appears to have taken place in the last several weeks. An Airbus image from Feb. 6, also released Thursday by Jane’s Defense Weekly, shows empty sand where the runway is now being built.

“We absolutely think it is for military aircraft, but of course an airstrip is an airstrip — anything can land on it if it’s long enough,” said James Hardy, Asia-Pacific editor for Jane’s Defense Weekly. “Three thousand meters is big enough for pretty much any aircraft.” He noted that the superjumbo Airbus A380’s runway requirement is 2,950 meters, or just under 10,000 feet.

Other runways used by the Chinese military have ranged from around 8,850 feet to more than 13,100, Mr. Hardy said. By comparison, he said, the runway the United States Air Force maintains at Diego Garcia, an island in the Indian Ocean that is much bigger and more developed than Fiery Cross Reef, is 11,800 feet.