Nanshan Island (Tagalog: Lawak, literally "vastness"; Chinese: 马欢岛; pinyin: Mahuan Dao; Vietnamese: Đảo Vĩnh Viễn) is the eighth largest natural island of the Spratly Islands group, and the fourth largest of the Philippine-occupied islands. (None of the Philippine-occupied islands have any significant amount of reclaimed land.) It has an area of 7.93 hectares (19.6 acres). It is located 98 miles (158 km) east of Thitu Island (Pag-asa). The island is administered by the Philippines as part of Kalayaan, Palawan.
This island is a bird sanctuary. Its surroundings are highly phosphatized that superphosphate materials can be mined out on a small-scale basis. Near the fringes of the breakwaters (approx. 2 miles (3 km) from the island), intact hard coral reefs were observed to retain their natural environment and beautiful tropical fishes were seen colonizing these coral beds of varying colors. It is also covered with coconut trees, bushes and grass. It is 580 m long, on the edge of a submerged reef.
A handful of Philippine soldiers and their families are stationed on the island, which has been inhabited since 1968 when Philippines occupied this island. There are only one to two structures in this island that serve as shelters for the soldiers. The soldiers are also the guard of nearby Flat Island which lies 6 miles (10 km) north-northeast of the island which is also occupied by the Philippines.