A ceremony was held in south China's Guangzhou for the launch of a China-Vietnam joint inspection of the waters outside the Beibu Gulf which is bordered by the two countries.
Chinese and Vietnamese experts will inspect the terrain and geological conditions outside the mouth of the Beibu Gulf.
The inspection will be carried out by China's Fendou No 5 ocean research vessel.
Xinhua described the Beibu Gulf as a half-closed bay surrounded by Chinese and Vietnamese territory and a traditional fishing area for the two countries.
More From This Section
In 2000, both countries signed agreements on the demarcation of the Beibu Gulf and fishing cooperation.
Vietnam along with the Philippines, Malaysia, Brunei and Taiwan have questioned Beijing's claims over almost all of the South China Sea.
An international tribunal constituted under the UN Convention on Law of Seas (UNCLOS) has admitted the Philippines' petition for arbitration though China boycotted the tribunal proceedings.
Vietnam too contemplated joining the arbitration but refrained after repeated appeals from China.
China and Vietnam agreed to launch the inspection when President Xi Jinping paid a state visit to Vietnam last month.
The inspection is an important beginning for maritime cooperation between the two countries, according to the joint statement issued after the visit.
China and Vietnam have been negotiating how to demarcate and develop the waters outside the mouth of the Beibu Gulf since 2012.
The launch of the joint inspection, which is the result of bilateral negotiation, shows that both countries are committed to solving maritime differences via cooperation in an appropriate way, the Chinese Foreign Ministry said.
"The two sides can clarify the resources and geology around the waters through joint inspection in order to lay a sound foundation for demarcation and joint development of the waters outside the mouth of the gulf," it said.
Representatives from the ministries of foreign affairs, surveying and mapping, land and resources of both countries attended the ceremony.