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

He was welcomed to Hanoi on 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.

Xi told Lam their two countries must "jointly oppose unilateral bullying, and uphold the stability of the global free trade system as well as industrial and supply chains," according to the Xinhua news agency.

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

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

Although the US 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 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" together.

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 Monday in Vietnam's state-run Nhan Dan newspaper.

Lam said in an article posted on the government's news portal 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 last year, with a bill of $161.9 billion, followed by Malaysia, which bought 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 governed by communist parties, already share a "comprehensive strategic partnership", Hanoi's highest diplomatic status.

Vietnam has long pursued a "bamboo diplomacy" approach that aims 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.

Xi said 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."

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".

In Malaysia, Communications Minister Fahmi Fadzil said Xi's imminent 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.

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