Where did the sand and gravel from the sea reclamation in Shenzhen come from?

Sand and stones at the bottom of the sea. The sand and gravel reclaimed from the sea in Shenzhen is sand and gravel from the seabed, which is reclaimed by cutter suction dredger. Shenzhen, referred to as Pengcheng for short, is a sub-provincial city, a city under separate state planning, a megacity in Guangdong Province, a China Special Economic Zone approved by the State Council, a national economic center city and an international city.