China and Vietnam signed dozens of cooperation agreements Monday, strengthening ties between the communist-run countries after Chinese leader Xi Jinping warned that protectionism "leads nowhere" and that a trade war would have "no winners".

Xi is in Vietnam for the first leg of a Southeast Asia tour, as Beijing tries to present itself as a stable alternative to an erratic US President Donald Trump, who announced -- and then mostly reversed -- sweeping tariffs this month.

The Chinese president was welcomed to Hanoi Monday with a 21-cannon salute, a guard of honour and rows of flag-waving children at the presidential palace, before holding talks with Vietnam's top leaders including General Secretary To Lam.

The two neighbours signed 45 cooperation agreements, including on supply chains, AI, joint maritime patrols and railway development.

Xi's visit comes almost two weeks after the United States -- manufacturing powerhouse Vietnam's biggest export market in the first three months of the year -- slapped a 46 percent levy on Vietnamese goods as part of a global trade blitz.

Although the reciprocal tariffs on Vietnam and most other countries have been paused, China still faces enormous levies and is seeking to tighten regional trade ties and offset their impact during Xi's first overseas trip of the year.

Xi will depart Vietnam on Tuesday, travelling onwards to Malaysia and Cambodia on a tour that "bears major importance" for the broader region, Beijing has said.

Speaking during a meeting with Lam, Xi said Vietnam and China were "standing at the turning point of history... and should move forward with joint hands".

Xi earlier urged the two countries to "resolutely safeguard the multilateral trading system, stable global industrial and supply chains, and open and cooperative international environment". 

He also reiterated Beijing's line that a "trade war and tariff war will produce no winner, and protectionism will lead nowhere" in an article published on Monday in Vietnam's major state-run Nhan Dan newspaper.

Vietnam's Lam said in an article posted on the government's news portal on Monday that his country "is always ready to join hands with China to make cooperation between the two countries more substantive, profound, balanced and sustainable".

- 'Bamboo diplomacy' -

Vietnam was Southeast Asia's biggest buyer of Chinese goods in 2024, with a bill of $161.9 billion, followed by Malaysia with Chinese imports worth $101.5 billion.

Firming up ties with Southeast Asian neighbours could also help offset the impact from a closed United States, the largest single recipient of Chinese goods last year.

Xi is visiting Vietnam for the first time since December 2023.

China and Vietnam, both ruled by communist parties, already share a "comprehensive strategic partnership", Hanoi's highest diplomatic status.

Vietnam has long pursued a "bamboo diplomacy" approach -- striving to stay on good terms with both China and the United States.

The two countries have close economic ties, but Hanoi shares US concerns about Beijing's increasing assertiveness in the contested South China Sea.

China claims almost all of the South China Sea as its own but this is disputed by the Philippines, Malaysia, Vietnam, Indonesia and Brunei.

The Chinese leader insisted in his article on Monday that Beijing and Hanoi could resolve those disputes through dialogue.

"We should properly manage differences and safeguard peace and stability in our region," Xi wrote.

"With vision, we are fully capable of properly settling maritime issues through consultation and negotiation," he said.

Vietnam's Lam said in his article that "joint efforts to control and satisfactorily resolve disagreements... is an important stabilising factor in the current complex and unpredictable international and regional situation".

After Vietnam, Xi will visit Malaysia from Tuesday to Thursday.

Malaysian Communications Minister Fahmi Fadzil said Xi's visit was "part of the government's efforts... to see better trade relations with various countries including China".

Xi will then travel to Cambodia, one of China's staunchest allies in Southeast Asia and where Beijing has extended its influence in recent years.