Investors in Asia shifted nervously on Friday as Donald Trump's much-hyped tax-cut plans hung in the balance after a plan to push them through hit unexpected hurdles.

The Dow surged to new records on Wall Street as several key Republicans backed the controversial reforms, which the president says will fire up the US economy, fuelling hopes they could reach Trump's desk for signing by year's end.

However, a new projection showing the measure would add $1 trillion to the federal deficit, complicating Trump's argument the cuts would pay for themselves, saw three Republican senators -- Bob Corker, Jeff Flake and Ron Johnson -- withdraw their support until changes were made.

Republicans hold a narrow 52-48 Senate majority and three defectors would kill the bill.