About 100 people rallied in Vietnam's capital, Hanoi, Sunday to protest China's recent actions in disputed regional waters.
Demonstrators shouted that the Spratly and Paracel islands belong to Vietnam, and they accused China of intending to invade Vietnam's territory.
Public protests are rare in communist Vietnam, but authorities have permitted the anti-China protests for a fifth consecutive Sunday.
Relations between the two Asian countries have been strained in recent weeks after Vietnam complained of aggressive behavior by Chinese vessels in the waters inside Vietnam's exclusive economic zone.
In mid-June, Vietnam held live-fire military drills in the South China Sea, but it described them as a routine exercise.
China has said the potentially resource-rich Spratly and Paracel islands and the surrounding waters are part of its territory. But the Philippines, Taiwan and Brunei also have territorial claims in the area.
Chinese and Vietnamese officials discussed the issue last week in Beijing. They said they would resolve the dispute through peaceful dialogue, but gave no other details.
The Vietnamese news agency quotes Chinese Ambassador Sun Guoxiang as saying that his country attaches importance to the traditional friendship with Vietnam and that it commits itself with the Vietnamese side to strengthen solidarity, cooperation and mutual support. It says the statement was made Friday, during a Hanoi event marking the 90th anniversary of the founding of the Communist Party of China.
Last month, Vietnam complained that a Chinese patrol ship severed an exploration cable trailing from an oil survey ship operating in waters inside Vietnam's exclusive economic zone. The Philippines also has complained of Chinese patrol boats interfering with oil exploration off its western coast.
In each case, China insisted its ships were operating appropriately in waters under Beijing's administration.
Some information for this report was provided by AFP and Reuters.