US President Donald Trump landed in Scotland on Friday for a five-day visit set to mix diplomacy, business and leisure, as a huge UK security operation swung into place amid planned protests near his family-owned golf resorts.

The president, whose mother was born in Scotland, will split his time between two seaside golf courses bearing his name, in Turnberry on the southwestern coast and Aberdeen in the northeast.

Air Force One, carrying the president and White House staff, touched down at Prestwick Airport near Glasgow shortly before 8:30 pm (1930 GMT).

Police officers lined surrounding streets and several hundred curious Scots came out hoping for a glimpse of the US leader as he made his way to Turnberry.

Trump has no public events scheduled for Saturday and is expected to play golf at his picturesque resort, before meeting EU chief Ursula von der Leyen on Sunday for trade talks.

Trump is also due to meet UK Prime Minister Keir Starmer during the trip.

"We're going to do a little celebrating together, because we got along very well," Trump told reporters as he left the White House on Friday, calling Starmer "a good guy" doing "a very good job."

He said they would discuss "fine tuning" the bilateral trade deal struck in May, and would "maybe even improve it."

But the unpredictable American leader appeared unwilling to cede to a UK request for reduced steel and aluminium tariffs.

Trump has exempted British exports from blanket 50 percent tariffs on both metals, but the fate of that carve-out remains unclear.

"If I do it for one, I have to do it for all," Trump told reporters, when asked if he had any "wiggle room" for the UK on the issue.

The international outcry over the conflict in Gaza may also be on the agenda, as Starmer faces growing pressure to follow French President Emmanuel Macron and announce that Britain will also recognise a Palestinian state. (AFP)