US President Donald Trump said on Friday he plans to announce tariffs on steel and semiconductors in the coming weeks.

"I'll be setting tariffs next week and the week after, on steel and, I would say, chips. Chips and semiconductors, we'll be setting sometime next week, the week after," Trump said on board Air Force One as he headed to Alaska for a summit with Russian President Vladimir Putin.

Trump said the levy rate would be "lower at the beginning" but "very high after a certain period of time," as a way to encourage businesses to relocate operations to the United States.

The president said his policy would prompt companies in key industries like automobiles and artificial intelligence to relocate in order to "beat the tariffs," which could be 200 or 300 percent.

Trump has also said he would employ this strategy with pharmaceuticals.

On August 6, Trump announced a 100 percent tariff on semiconductors from firms that do not invest in the US.

Trump has already instituted tariffs on steel, announcing an initial 25 percent levy that was later doubled to 50 percent. (AFP)