President Donald Trump has said the US will soon announce a "major" tariff on pharmaceutical imports and accused China of manipulating its currency to offset Washington's levies.

Speaking at an event at the National Republican Congressional Committee on Tuesday, Trump said the tariff will incentivise drug companies to move their operations to the US.

"We are going to be announcing very shortly a major tariff on pharmaceuticals," Trump said in remarks at a National Republican Congressional Committee dinner.

"Once we do that, they're going to come rushing back into our country because we're the big market. The advantage we have over everybody is that we're the big market," he said.

"When they hear that, they will leave China, they will leave other places, because they have to sell — most of their product is sold here," he added, referring to drug companies.

'Unjustified' tariffs

Trump also accused China of manipulating its currency to offset the impact of US tariffs and imposing "unjustified" tariffs.

"You got to hand it to them. They're manipulating their currency today as an offset against the tariffs," Trump said.

"They all got rich because of tariffs. You know, now, when we do it all, it's so terrible. 'What Trump is doing, it's so terrible.' They got rich, and not only China. Many countries. I mean, you look at Vietnam, you look at so many — I could name 50 right now."

Trump noted that a 104 percent tariff on Chinese goods would take effect at midnight, adding they would remain in place until Beijing agrees to a new deal.

"I think they'll make a deal at some point," he said, "China will. They want to make a deal. They really do."