Trump was in the communist capital at the tail end of his swing through Asia where he has promoted his "America First" mantra on global trade, prioritising "fair" bilateral deals over sprawling multilateral pacts.
Several agreements were signed during his state visit Sunday, including in the natural gas sector, transport and aviation.
National carrier Vietnam Airlines signed a deal worth USD 1.5 billion for engines and support services from US firm Pratt & Whitney, which the airline said would boost US-Vietnam ties.
Trump is seeking to boost exports of American goods and services as part of a campaign pledge that ushered him into office with hefty support from blue-collar workers in the United States.
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He has accused Vietnam and China, two key Asian manufacturing hubs, of "stealing" American jobs and blamed for previous US administrations for allowing trade deficits to grow unchecked.
On Sunday he again complained about the United States' gaping trade deficit with Vietnam, worth $32 billion in 2016.
"We have to take care of American companies and we have to take care of American workers," he added in comments likely to play well among his base back home.
American energy firms Alaska Gasline Development Corporation and AES Corporation also signed deals Sunday, along with US truck company Navistar and Vietnamese budget airline VietJet, though no details were provided.
Vietnam has eagerly sought to drum up trade and investment with the United States since Trump came to power, especially after he withdrew from the massive Trans-Pacific Partnership free trade deal that Vietnam stood to gain enormously from.
American exports to Vietnam have soared in the past decade, increasing ninefold to more than $10 billion in 2016, according to official figures from the US Trade Representative. Vietnam's exports to the United States over the same period rose around fivefold.
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