US President Barack Obama said China must stop land reclamation in disputed waters in the South China Sea.
He was speaking on the sidelines of an economic summit of Asia Pacific nations (Apec), which opened in Manila.
Mr Obama earlier pledged monetary and naval assistance to the Philippines, which has competing claims with China in the resource-rich region.
China – which claims most of the South China Sea – has repeatedly stated that its dredging work is legal.
The land reclamation, which began in late 2013, has turned submerged reefs into islands. China has said it has “no intention to militarise” those islands.