A look at the countries' shared history and some most recent ups and downs in relations. Divided opinions within Vietnam's Communist Party on how to relate to giant neighbor and one-time ally China are among key factors in play at an eight-day congress to choose new leadership.
Longtime rivalsVietnam and China have a complex relationship going back more than 2,000 years, including several periods of Chinese imperial occupation that were ended by Vietnamese uprisings.
Despite its early support for the Vietnamese Communist Party, China invaded in 1979 in retaliation for Hanoi's overthrow of the Khmer Rouge in Cambodia. Diplomatic ties were restored in 1991, but tensions have risen in recent years due to competing claims to islands and reefs in the South China Sea.
Keeping watch China is closely observing the party congress and has emphasized the importance of China-Vietnam relations, including $90 billion in bilateral trade last year."As a good neighbor, friend, comrade and partner to Vietnam, we wish to advance the overall strategic relationship into a new stage on the basis of long-term stability, forward thinking and good neighborliness," Foreign Ministry spokesman Hong Lei said Friday."We also wish to work with Vietnam to appropriately control maritime disputes with Vietnam so as to safeguard the maritime stability."
Oil rig dispute In May 2014, China parked a huge oil drilling platform off the Vietnamese coast in an area where the two countries' exclusive economic zones overlap. Vietnam furiously denounced the move and sent fishing boats and coast guard vessels to harass the rig and nearby Chinese vessels. Skirmishes led to collisions and the capsizing of at least one Vietnamese boat, while in Vietnam anti-Chinese rioting and the looting of Chinese and other foreign-owned factories left at least four Chinese citizens dead.
China's outreachChinese Foreign Minister Yang Jiechi visited Vietnam in June 2014 to try to contain the oil rig dispute.
Despite receiving a frosty reception from Vietnamese Prime Minister Nguyen Tan Dung, escalation was avoided. More significantly, the oil rig incident nudged Vietnam closer to its old enemy the United States, which later that year partially lifted an arms embargo specifically to help improve Vietnam's maritime security.
Competing claimsChina withdrew the rig in July 2014, one month ahead of schedule, saying it had completed its mission.
The confrontation is widely seen as part of a Chinese strategy to strengthen its footprint in the South China Sea, all or part of which is also claimed by Vietnam, the Philippines, Taiwan, Malaysia and Brunei.
The incident also focuses renewed attention on a perceived split within the Vietnamese Communist Party between pro- and anti-China factions.
Vietnam visitsFollowing a prolonged chill, Communist Party chief Nguyen Phu Trong (pronounced NEW-yen FOO CHONG) led a delegation to Beijing in April 2015 and was greeted by President Xi Jinping with full military honors at the Great Hall of the People. Though little of substance resulted from the four-day trip visit, it is seen as helping get relations back on track.
Mending tiesChina's Xi made a state visit to Vietnam in November 2015, during which he and Trong agree to limit their differences and maintain peace and stability.Xi said China will "strive together with Vietnam to control differences at sea." Trong proposed that neither side take actions that increase tensions.
During the visit, about 30 people protested briefly in front of the Chinese Embassy in Hanoi. Xi also addressed Vietnam's National Assembly, but avoided mentioning the South China Sea and the 1979 war.
Tensions renewedVietnam protested to China in January over a test flight to a new airstrip on one of Beijing's man-made island in the disputed Spratly Islands.
Vietnam Foreign Ministry spokesman Le Hai Binh demanded an end to such flights, saying they violate Vietnam's sovereignty and hurt bilateral relations. China responded that the flights fall "completely within China's sovereignty." Days later, China conducted two more test flights. The South China Sea dispute looks only to grow more complex as China completes infrastructure on its newly created islands and boosts its maritime defense forces beyond anything its rival claimants can muster.
Christoper Bodeen, Associated Press, Beijing