Southeast Asian leaders have said land reclamation projects in the South China Sea risk undermining regional peace.
The leaders' statement comes at the end of a regional summit but a draft was widely reported on Monday.
Though it does not mention China, it comes after satellite images showed extensive Chinese building in disputed parts of the sea.
China claims almost the whole of the South China Sea, resulting in overlapping claims with its neighbours.
Those countries whose claims overlap China accuse it of illegally taking land to create artificial islands with facilities that could potentially be for military use.
China - which is not in Asean but is a major trading partner of many members - says its work is legal and needed to safeguard its sovereignty.