US President Donald Trump's raft of "Liberation Day" tariffs will take effect immediately after he unveils them on Wednesday, White House Press Secretary Karoline Leavitt said.

"My understanding is that the tariff announcement will come tomorrow, they will be effective immediately," Leavitt told reporters on Tuesday, adding she had just spoken to Trump about the issue.

Trump's forthcoming imposition of reciprocal tariffs on nations worldwide will serve as a major milestone in US history, the White House said.

"Tomorrow, April 2, 2025, will go down as one of the most important days in modern American history," spokesperson Karoline Leavitt told reporters.

"Our country has been one of the most open economies in the world, and we have the consumer base, hands down the best consumer base, but too many foreign countries have their markets closed to our exports. This is fundamentally unfair," she added.

Leavitt maintained that the import duties will be "effective immediately" after the president's announcement Wednesday, but much remains unclear about the forthcoming policy.

Markets have fallen sharply lower on news that Trump intends to impose reciprocal tariffs on countries across the globe April 2 -- a day he has dubbed "Liberation Day."

The tech-heavy Nasdaq has shed more than 2,500 points since February when Trump first teased his intention while the Dow is down nearly 3,000 points.