The Philippines has begun long-delayed repairs to a crumbling runway on the largest of its nine outposts in the South China Sea.
Satellite images taken on May 17 and released on Friday by the Washington-based Asia Maritime Transparency Initiative (Amti) showed two barges with a grab dredger and a backhoe at the sea-swept end of the 1.3km runway on Thitu island.
The runway was supposed to have been repaired as early as April last year, but the plan was stalled by concerns over how China would react.
China had, in the past, used its Coast Guard fleet to block efforts by the Philippines to resupply and upgrade its outposts in the Spratly island chain in the southern end of the South China Sea.
China claims almost the entire South China Sea, a strategic waterway through which about US$3 trillion (S$4 trillion) worth of sea-borne goods passes every year. Vietnam, Malaysia, Brunei and Taiwan also have conflicting claims in the area.
The Philippines won a case in 2016 before an international tribunal dismissing China's claims. But President Rodrigo Duterte has opted to set aside this victory. He said last week he would rather not provoke China because that could only lead to "a war we cannot win".
Thitu houses about a hundred civilians and a small contingent of soldiers. The island's runway was the first built in the Spratlys. But the sea, over time, has eroded about 100m of its western end. The runway's surface has also become too soft to land on whenever it rains.
Ongoing repairs on Thitu are "consistent with our national sovereignty and jurisdiction", Mr Duterte's spokesman Harry Roque said in a text message yesterday.
Thitu houses about a hundred civilians and a small contingent of soldiers.
The island's runway was the first built in the Spratlys. But the sea, over time, has eroded about 100m of its western end. The runway's surface has also become too soft to land on whenever it rains.
Apart from repairing the runway, the Philippines has also built at least seven new buildings on Thitu, Amti reported.
Minor improvements, meanwhile, were seen on three other Philippine outposts.
A new round-roofed shelter has been built on the eastern side of Commodore Reef.
An empty field on Nanshan island has been converted into a helipad, and an additional hexagonal shelter has been built on Loaita Cay, a small sandbar.
Vietnam and Taiwan have also made improvements to their outposts in the Spratlys. But these have been dwarfed by the scale and development undertaken by China.
Just 12 nautical miles off Thitu, China's outpost on Subi reef has nearly 400 individual buildings.
Subi is the largest of China's seven man-made islands in the Spratlys.
The so-called Big Three of Subi, Mischief and Fiery Cross reefs all share similar infrastructure, including emplacements for missiles, 3km runways, extensive storage facilities and a range of installations that can track satellites, foreign military activity and communications.
Mischief and Fiery Cross each house almost 190 individual buildings and structures.
Analysts said the facilities on Subi, Mischief and Fiery Cross could each hold a regiment - between 1,500 and 2,400 troops.
Subi could be the future location of hundreds of People's Liberation Army marines, as well as a possible administrative hub as China cements its claim with a civilian presence, security analysts and diplomatic sources told Reuters.