HANOI (AFP) - Vietnam and the United States signed a raft of energy and aviation deals on Sunday (Nov 12) during a visit to Hanoi by US president Donald Trump who railed against Washington's yawning trade deficit with the fast-growing nation.

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 on Sunday, including in the natural gas sector, transport and aviation.

National carrier Vietnam Airlines signed a deal worth US$1.5 billion for engines and support services from US firm Pratt & Whitney, which the airline said would boost US-Vietnam ties.

"(The agreement) will further reinforce the important economic, trade and investment partnership between Vietnam and the United States," Vietnam Airlines CEO Duong Tri Thanh said in a statement.

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.

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 US$32 billion in 2016.

"We have to get rid of the trading imbalance, we can't have a trade imbalance," he said at the beginning of a meeting with Vietnamese Prime Minister Nguyen Xuan Phuc.

"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.

"And perhaps administrations previous to me didn't like the subject, understand the subject. Something was wrong because so many problems having to do with trade imbalance so we want to get that straightened out very quickly."

Trump then went on to suggest that Vietnam buy American military gear, aircraft and missiles.

"We would like you to buy your equipment from the United States," Trump said in comments reported by CNN.

"We make the best equipment. We make the best military gear, and planes, and anything you can name. The missiles are in a category that no ones even comes close."

Trump described how a US-made Patriot missile defence system recently intercepted a Yemeni-made missile that was shot over Saudi Arabia's capital.

"I told before as you know, a missile was shot into Saudi Arabia recently from Yemen, and one of our missile systems knocked it down, nobody even knew what happened. And missile exploded in air, knocked it down like nothing. We make the greatest missiles in the world, greatest planes in the world, greatest commercial air craft in the world. So we would like Vietnam to buy from us, and we have to get rid of the trade imbalance. We can't have the trade imbalance."

Trump also made a similar sales pitch in Japan, the first stop of his 12-day Asia tour which started on Nov 5.

He said to that the purchase of American military equipment would bring employment to the US and safety to Japan.

He said during a joint press conference with Japan's prime minister Shinzo Abe that he expects Tokyo to shoot down any missiles fired by North Korea over its territory "once it completes the purchase of US military equipment".

Vietnam, the fourth leg of Trump's Asia tour after stops in Japan, South Korea and China, has eagerly sought to drum up trade and investment with the US 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.

The US is a leading export market for Vietnam, where a booming manufacturing sector has largely driven dizzying economic growth in recent years.

American exports to Vietnam have soared in the past decade, increasing ninefold to more than US$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.

American energy firms Alaska Gasline Development Corporation and AES Corporation also signed deals on Sunday, along with US truck company Navistar and Vietnamese budget airline VietJet, though no details were provided.