Vietnam is holding military exercises with live rounds off its coast, as it accuses Beijing of raising tension in the South China Sea.
A war of words between both countries has been building for weeks, with claims of intrusions into each other’s territorial waters.
The disputed Spratley and Paricel archipelagos are at the heart of a long-running row, with maritime disputes also involving the Philippines, Malaysia, Brunei and Taiwan.
Public protest is rare in Vietnam, but authorities have allowed a second day of anti-China demonstrations.
Observers say a military clash between China and Vietnam is unlikely, but the tension will set back diplomatic efforts to improve regional relations.