President Xi Jinping met with Vietnamese Communist Party chief Nguyen Phu Trong during a state visit to Hanoi on Sunday, after Trump also visited the country.
The Chinese and Vietnamese sides "reached an important consensus in accordance with leaders of the two parties and countries, to appropriately manage maritime issues, steadily advance all forms of maritime cooperation including joint development and jointly strive to uphold peace and stability in the South China Sea," Xinhua news Agency reported.
No further details were provided.
China claims nearly all of the strategically vital sea, through which US$5 trillion (HK$39 trillion) in shipping trade passes annually. It is also tipped to sit atop vast oil and gas deposits.
Vietnam, the Philippines, Malaysia, Brunei and Taiwan also have claims in the sea, and the dispute has long been seen as a potential trigger for conflict in Asia.
Days after Trump met with Xi in Beijing, the former made a surprise offer to Vietnamese President Tran Dai Quang in Hanoi.
"If I can help mediate or arbitrate, please let me know I am a very good mediator," Trump said.
The offer could irritate the Chinese government, which has repeatedly said the United States has no role to play in what it insists is a series of bilateral issues.
Vietnam has courted support from Washington in the row amid Beijing's bid to cement its claims in the disputed areas.
In Manila, Southeast Asian nations said it will not take the relative calm in the sea dispute for granted, according to a draft of a statement to be issued yesterday. The statement will be issued after a meeting between China and the 10-member Association of Southeast Asian Nations in Manila, a diplomatic source said.
"While the situation is calmer now, we cannot take the current progress for granted," said the draft. "It is in our collective interest to avoid miscalculations that could lead to escalation of tensions."
AGENCE FRANCE-PRESSE, REUTERS