MELBOURNE, Australia — China is continuing to expand its construction activities in a second group of disputed South China Sea islands, according to a Washington-based think tank on Wednesday.

The report, released Wednesday by the Center for Strategic and International Studies' Asia Maritime Transparency Initiative, says Beijing has undertaken substantial upgrades to its military infrastructure in the Paracel Islands, with the construction of harbors, helipads and a full-fledged helicopter base on several islands in the chain.

Also claimed by Vietnam, the Paracels already play a key role in China's goal of establishing surveillance and power projection capabilities throughout the South China Sea. Their location, less than 200 miles from the southern Chinese island of Hainan, means that bases and facilities on the Paracels can serve to bridge the distance between Hainan and outposts farther south.

China occupies 20 outposts in the Paracels, of which it gained total control after a series of skirmishes with the former South Vietnam in 1974. The islands lie farther north of the more well-known Spratly Islands, and are referred to as the Xisha Islands by the Chinese. 

The latest satellite imagery obtained by CSIS-AMTI think tank show that five of the island outposts contain helipads, with Duncan Island housing a full helicopter base while the Triton, Money and Pattle islands each boast a single helipad to add to helicopter facilities on China's main Paracel base on Woody Island.

This infographic shows the reported buildup of military infrastructure on the Paracels by China.

Photo Credit: Courtesy of CSIS/AMTI

CSIS-AMTI suggests the Duncan Island heliport could play an important role in Chinese anti-submarine warfare efforts in the region, although it is also possible that helicopters based there could be used to service the less well-equipped outposts in the Paracels.

In addition, large harbors have also been expanded or dredged at Palm and Duncan islands as well as Tree Island. Smaller harbors also exist on several smaller Paracel islands, with some having been built only in the last few years. Dredging and construction on several other islands on the Paracels have been observed on the satellite imagery obtained by CSIS-AMTI, suggesting that China intends to carry out more work to add to the facilities in the Paracels.

These new structures are in addition to Woody Island, which is now China’s main base in the Paracels. The airbase and first structures were built in the 1990s, and since then China has "undertaken substantial land reclamation to expand Woody Island and construct new facilities," according to CSIS-AMTI. This includes an upgraded "air base to include 16 small hangars for combat aircraft as well as four larger hangars."

Defense News believes that the former are climate-controlled to better protect aircraft from the humid, salty environment. The two sheltered harbors on the island have also received substantial upgrades, while HQ-9 and anti-ship cruise missiles have also been deployed on site.