HANOI (AFP) - US President-elect Donald Trump has reassured Vietnam over future ties, according to the communist nation, which is set to lose out if he honours a vow to ditch a major trade deal.

In a phone call on Wednesday (Dec 14) with Vietnamese Prime Minister Nguyen Xuan Phuc, Trump "affirmed the wish to cooperate with Vietnam to strengthen bilateral ties".

The Vietnamese leader congratulated Trump on his November election win and said he honours the "friendly and cooperative" ties with Washington, according to a statement posted on the Vietnam government website.

"The two leaders exchanged ideas and measures to promote Vietnam-US economic, commercial and investment relations in the future," the statement added.

Ties between the former foes have warmed steadily since the end of the Vietnam War, especially under outgoing president Barack Obama who has championed a so-called pivot to Asia policy.

A pillar of that policy was the Trans-Pacific Partnership (TPP), a massive global trade pact that Trump has said he will scrap on his first day in office.

He has said the TPP would harm US manufacturing and jobs.

Manufacturing hub Vietnam stands to gain enormously from the 12-country deal, which would reduce tariffs and open Vietnam's access to key markets like the United States and Japan.

Many economists argued that low-wage Vietnam could add more than 10 per cent to its GDP over a decade under the deal.

But it must be ratified by all signatories to come into effect.

Vietnam has said it is still committed to existing trade deals, including with the United States, regardless of what happens with the TPP.

Japan's parliament ratified the agreement this month despite Trump's opposition.

Trump is expected to travel to Vietnam in November 2017 for the annual APEC summit.

Obama received a hero's welcome during a May visit to Vietnam, where he sat down for a bowl of noodles and fielded questions from adoring students between high-level meetings with officials.