The top US trade official on Tuesday defended President Donald Trump's sweeping tariffs on nearly every other nation, telling US senators that with dozens of countries seeking a deal the strategy was "already bearing fruit."

Jamieson Greer's appearance in Congress came with Republicans ringing alarm bells over Trump's escalating trade war and Wall Street clamoring for clarity on the president's plans after a historic market sell-off.

"Nearly 50 countries have approached me personally to discuss the president's new policy and explore how to achieve reciprocity," he told the Senate Finance Committee, a figure that other administration officials have also cited. 

Several countries -- including Argentina, Vietnam and Israel — had offered to reduce their tariffs, Greer said, while auto manufacturers were canceling layoffs and companies had announced $4 trillion in new investment in the United States.

The annual hearings on the president's trade policies are often staid affairs.

But they have generated more interest this year after Trump last week announced a baseline tariff of 10 percent and extra levies of up to 50 percent on countries selling more to Americans than they buy in return.

Greer said the country had shed five million manufacturing jobs and 90,000 factories in the last 30 years, since a trilateral free trade agreement with Mexico and Canada was enacted.

"We must move away from an economy based solely on the financial sector and government spending, and we must become an economy based on producing real goods and services," he added.

Senior Republican lawmakers have pledged to allow Trump time to see how his tariff gambit plays out, but are desperate to see progress on trade negotiations they believe will calm markets. 

Wall Street stocks surged higher early Tuesday after a three-day rout as global markets rallied in hopes of trade agreements.

'No clear message'

But rank-and-file lawmakers remain jittery about the effect of the tariffs and have been demanding briefings on the strategy, with some even seeking to remove Trump's authority to raise import levies.

Republican Senator Chuck Grassley is leading a bipartisan effort to require congressional approval of tariffs within 60 days, although it is not expected to get a floor vote.

Four Republican senators voted with Democrats last week to pass a symbolic resolution to undo Trump's tariff on Canada that does not have the force of law.

Trump himself ruled out any pause in his aggressive new global trade policy on Monday, and threatened to slap an additional 50 percent tariff on China over its retaliation.

He also dismissed the possibility of a trade deal with the European Union and called his critics on trade "weak and stupid" while pledging to veto Grassley's bill.

The top Democrat on the finance committee, Ron Wyden, assailed the White House for having "no clear message" about how Trump determined his tariffs and how long he plans to keep them up. 

He suggested Trump was deliberately tanking the economy to bring down interest rates, making borrowing cheaper for the rich.

Greer never had much hope of persuading Democrats over Trump's trade policies, but his overtures did not appear to reassure skeptics on the Republican side either.

"Whose throat do I get to choke if this proves to be wrong?" asked North Carolina free trade advocate Thom Tillis.

Greer's appearance was the first of two annual hearings on the president's trade policies. He will be grilled by the House Ways and Means Committee on Wednesday.