US President Donald Trump said on Tuesday that he would not extend an August 1 deadline for higher US tariffs to take effect on dozens of economies, while announcing plans for a 50 percent duty on copper imports.

The copper levy would come after a probe into imports of the metal, broadening a slate of sector-specific tariffs Trump has imposed since returning to the White House.

"Today we're doing copper," he told a cabinet meeting on Tuesday. "I believe the tariff on copper, we're going to make it 50 percent."

Commerce Secretary Howard Lutnick told CNBC shortly afterward that the rate will likely be implemented at the end of July or on August 1.

Trump also said Washington would soon make an announcement on pharmaceuticals, but officials would allow manufacturers time to relocate their operations into the country.

"We're going to give people about a year, a year and a half to come in, and after that, they're going to be tariffed," he said. "They're going to be tariffed at a very, very high rate, like 200 percent."

Apart from copper and pharmaceuticals, Trump has ordered probes into imports of lumber, semiconductors and critical minerals that could lead to further levies.

Lutnick told CNBC that US studies on pharmaceuticals and semiconductors would be completed by the end of the month, with Trump to set policies thereafter.

Beyond tariffs impacting sectors, Trump separately slapped a sweeping 10 percent tariff on goods from almost all trading partners in April.

These would have swiftly risen to steeper levels for dozens of economies including the European Union and Japan, but Trump paused their implementation until July 9.

The president this week again delayed their reimposition, pushing it to August 1 while insisting there would be no further delay. (AFP)