Demonstrations have been held in Vietnam against Chinese naval operations in disputed waters of the South China Sea.
The protests in Hanoi and Ho Chi Minh City follow a confrontation last month between a Vietnamese survey ship and Chinese patrol boats.
China, Vietnam, the Philippines, Malaysia, Brunei and Taiwan all claim territories in the South China Sea.
The BBC reports that tensions between China and Vietnam escalated after an incident on 26 May in which Hanoi accused a Chinese patrol of cutting the cables of a Vietnamese seismic research ship about 120km off the coast of Vietnam.
Public protests happen rarely in Vietnam, but calls for demonstrations have spread on the internet and via mobile phones in the past few days.
On Sunday, the protesters in Hanoi shouted slogans including ''The Paracels and Spratlys belong to Vietnam'', a reference to two groups of islands claimed by both countries.
They also carried signs that read: ''Stop Chinese invasion of Vietnam's islands''.
The BBC reports they marched to the Chinese embassy, where police watched them for a time before leading them away.