The head of the Asian Development Bank on Thursday urged Washington to remain engaged with Asia, days after US President-elect Donald Trump vowed to scrap a trans-pacific trade pact.

Takehiko Nakao told reporters the incoming US leader had previously talked about the importance of the "trade relationship".

He added, "it's important for the United States to continue to engage in Asia and that is good for the Asian region as a whole".

The US-led Trans-Pacific Trade Partnership (TPP), promoted by outgoing US President Barack Obama as part of his Asia pivot, liberalises inter-regional trade among 12 countries but Trump has charged it will cost the US jobs and hurt American businesses.

The president-elect said earlier this week he would ditch the TPP on his first day in the White House.

But Nakao cited the ASEAN Economic Community (AEC) as well as the China-endorsed Regional Comprehensive Economic Partnership (RCEP) as regional trade arrangements that could still prosper even if the TPP fails.

"There is a strong case for certain regional arrangements," he said.

Nakao defended open trade, saying it had helped Asia develop in recent decades.

"We should look at how the world has become a better place for many people from many countries," he added.

Critics have said a US withdrawal would make the TPP meaningless and amount to Washington abdicating its leadership role in the region.