Vietnam's foreign ministry has accused China of increasing regional tensions in an escalating territorial dispute.
A rare weekend news briefing followed a confrontation in the South China Sea between a Vietnamese oil and gas survey ship and Chinese patrol boats.
Vietnam says the boats deliberately cut the survey ship's cables in Vietnamese waters. China denies the allegation.
China, Vietnam, the Philippines, Malaysia, Brunei and Taiwan all claim territories in the South China Sea.
The area includes an important shipping route and is also thought to contain oil and gas deposits.
The spat comes just days before a regional security conference in Singapore.
Beijing said its defence minister would attend the IISS Asia Security Summit, the Shangri-La Dialogue, to promote co-operation and stability in the Asia Pacific region.
The latest clash involving Chinese patrol boats occurred 120km (80 miles) off the south-central coast of Vietnam and some 600km south of China's Hainan island.
"The Vietnamese navy will do everything necessary to firmly protect peace and the independence, sovereignty and territorial integrity of Vietnam," foreign ministry spokeswoman Nguyen Phuong Nga said.
One of three Chinese patrol vessels on the scene intentionally cut a submerged cable towed by the ship, the Binh Minh 02, said Do Van Hau, deputy chief executive of state oil and gas group PetroVietnam, which was operating the ship.
"Chinese vessels were at very high speed and did not respond to our ship's warning and then cut the cables of the Binh Minh 02, about 2km from where it was positioned," he said.
China's foreign ministry blamed Vietnam for the incident, saying its oil and gas operations "undermined China's interests and jurisdictional rights".
China's claim in the South China Sea is by far the largest, and includes the Spratly and Paracel archipelagos.
Taiwan recently said it would improve the defence capability of more than 100 coastguard troops stationed in a disputed area of the South China Sea.
Taiwan's decision was announced shortly after the Philippines increased the pressure recently by lodging a protest at the United Nations against China's claims to the area.
Last year, China sharply rebuked US Secretary of State Hillary Clinton when she said the US supported the freedom of navigation in the area and offered to facilitate multilateral talks on the disputes.