China claims virtually the entire South China Sea as its own, denying the claims of others and defying an international ruling invalidating its assertion.

The work on Triton Island in the Paracel group mirrors construction on seven human-made islands in the Spratly group to the east which have been equipped with airstrips, docks and military systems, although it currently appears to be somewhat more modest in scale.

China appears to be constructing an airstrip on a disputed South China Sea island that is also claimed by Vietnam and Taiwan, according to satellite photos analyzed by The Associated Press.

Satellite photos from Planet Labs PBC analyzed by the AP show construction on the airstrip first visible in early August. The runway, as currently laid out, would be more than 600 meters long, long enough to accommodate turboprop aircraft and drones, but not fighter jets or bombers.

Also visible are large numbers of vehicle tracks running across much of the island, along with what appear to be containers and construction equipment.

Triton is one of the major islands in the Paracel group, which is roughly equidistant from the coast of Vietnam and China's island province of Hainan.

The U.S. takes no stance on the sovereignty claims, but regularly sends Navy ships on "freedom of navigation operations" near the Chinese-held islands. Triton was the focus of one of those missions in 2018.

China has had a small harbor and buildings on the island for years, along with a helipad and radar arrays. Two large fields on the island sport a star from the Chinese flag and a hammer and sickle representing the ruling Communist Party.

China has refused to provide details of its island construction work other than to say it is aimed at helping global navigation safety. It has rejected accusations that it is militarizing the crucial waterway, through which an estimated $5 trillion in trade passes annually, and says it has the right to do as it wishes in its sovereign territory.

China seized full control of the Paracels from Vietnam in a brief 1974 naval conflict.