Los Angeles: President Donald Trump will slap import quotas on Australian steel and aluminium and the tariff exemption he granted Prime Minister Malcolm Turnbull may only be temporary.

US Trade Representative Robert Lighthizer and Mr Trump's policy adviser Peter Navarro offered new details on the tariffs on Thursday, US time.

Australia, Europe, South Korea, Canada, Mexico, Argentina and Brazil were named by Mr Lighthizer as the nations that will initially escape America's 25 per cent steel and 10 per cent aluminium tariffs, which come into force on Friday.

The Trump administration, however, was quick to remind Australia and the other exempted countries pressure would be applied to secure better trade deals for the US.

"Here's what's going to happen," Mr Navarro told CNN.