US President Donald Trump has signalled that fresh tariffs on imported pharmaceuticals and semiconductors could be unveiled within the coming week, amid a cascade of incoming duties.

Governments around the world are bracing as new waves of US tariffs are due to take effect this week, first on many Brazilian products on Wednesday and then on dozens of other economies a day later.

Trump's sweeping plans have sparked a flurry of activity as leaders seek to avert the worst of his threats, with Swiss officials heading to Washington on Tuesday in a last-minute push to avoid punitive duties.

But the US president appears set to widen his trade wars.

Trump told CNBC that upcoming tariffs on imported pharmaceuticals could reach 250 percent, while adding that he plans for new duties on foreign semiconductors soon.

"We'll be putting (an) initially small tariff on pharmaceuticals, but in one year, one-and-a-half years, maximum, it's going to go to 150 percent," Trump said.

"And then it's going to go to 250 percent because we want pharmaceuticals made in our country."

Trump also said that Washington will be announcing tariffs "within the next week or so."

He added: "We're going to be announcing on semiconductors and chips."

Trump has set out varying tariff rates for dozens of economies after imposing a 10-percent levy on almost all trading partners in April.

But these broad duties taking effect on Thursday exclude products like pharmaceuticals, steel, aluminium and lumber, which are being separately targeted by sector.

This means that although the 39-percent tariff Swiss leaders seek to avoid come Thursday excludes pharmaceuticals, Trump's plans for a steep levy on such imports will likely remain a point of contention in any talks.

Pharmaceuticals represented 60 percent of Swiss goods exports to the United States last year.

Outside of Switzerland, most products from the European Union face a 15 percent tariff starting on Thursday, after Washington and Brussels struck a deal to avoid higher levies.

But Trump warned on Tuesday that the EU could see its tariff level surge again if it did not fulfil obligations under their recent pact.

Some imports from Canada are also targeted by tariffs, although Prime Minister Mark Carney stressed on Tuesday that more than 85 percent of trade between the North American neighbours remains tariff-free under existing exemptions.

Besides probing pharmaceuticals and chips imports, Trump has already imposed steep duties of 50 percent on steel and aluminium, alongside lower levies on autos and parts.

In the same CNBC interview on Tuesday, Trump said he expects to raise the US tariff on Indian imports "very substantially over the next 24 hours" due to the country's purchases of Russian oil.

His pressure on India comes after signalling fresh sanctions on Moscow if it did not make progress by Friday towards a peace deal with Kyiv.

US envoy Steve Witkoff will meet on Wednesday with Russian leadership in Moscow. (AFP)