Tension between two has been on the rise since last month when Vietnam accused Chinese patrol boats of harassing an oil-exploration ship conducting a seismic survey 120 km (80 miles) off Vietnam’s south-central coast.
The two countries, which fought a brief but intense war on their land border in 1979, have exchanged accusations and re-staked long-standing claims of sovereignty over maritime territory which covers important shipping routes and may hold large, untapped oil and gas reserves. 
Public protests are rare in Vietnam. As well as the procession of banner-waving people in the capital, images posted online showed about 1,000 people marching in what appeared to be a similar protest in Ho Chi Minh City, Vietnam’s commercial hub.
The demonstrators in Hanoi sang patriotic songs and chanted slogans including “The Paracels and Spratlys belong to Vietnam,” referring to two largely uninhabited archipelagos claimed by both countries.
“China’s actions are immoral and not something such a powerful nation should do. Vietnam wants a friendly relationship with China but does not tolerate China’s disrespectful, invasive and bullying attitude,” said one protester, Dao Minh Chau.
Two people carried a Chinese flag emblazoned with a pirate’s skull and crossbones.
The protests were the first of their kind since December 2007 when widespread anger about China’s growing assertiveness over its claims to the Paracels and Spratlys drew hundreds of people out in Hanoi.
Maritime disputes are a sensitive topic for the Vietnamese government which tries to strike a balance between appeasing a populace that is deeply suspicious of China and keeping relations its giant neighbor from souring.
Hanoi police watched the peaceful protest and after a while led the demonstrators away from a park in front of the Chinese embassy.
The Philippines, Malaysia, Brunei and Taiwan also claim territories in the South China Sea, but China’s claim is by far the largest, forming a vast U-shape over most of the sea’s 648,000 sq miles (1.7 million sq km).
The latest tension comes as defense ministers from around the region met in Singapore for an annual security dialogue.
Chinese Defense Minister Liang Guanglie told his Vietnamese counterpart Phung Quang Thanh at the conference on Saturday that their countries should resolve their disputes peacefully.
Vietnam had said it would use its navy to enforce its territorial integrity.