The agreement comes at a time of simmering tension in the South China Sea and international concern about an escalation, and over the conduct of China’s vast fleet of coast guards and its activities in the exclusive economic zones of its neighbours.
Vietnam has a tricky balancing act of opposing actions by China that it deems infringements on its sovereignty, while needing to maintain close relations with its giant neighbour, forged over decades by their ruling Communist Parties.
Vietnam’s decision to enter into the agreement comes at a time when US defence ally the Philippines and China are sparring almost every week over the South China Sea, a row that has raged for more than a year.
China claims sovereignty over almost all of the strategic waterway.
Despite their overlapping claims in the Spratly Islands in the South China Sea, where Vietnam and the Philippines each occupies atolls and reefs, both countries have expressed desire to work together and tackle disputes.
Coast guards of the two countries earlier this month held their first-ever joint exercises in Manila, simulating fire-fighting drills and search-and-rescue exercises.
That came after Marcos visited Hanoi in January and signed deals that covered “incident prevention in the South China Sea” and “maritime cooperation”.
