Opponents of Donald Trump have inflated a balloon depicting the US President as an orange, snarling baby on the second day of his visit to the UK.

The controversial protest outside the Houses of Parliament was given the go ahead by London's Mayor Sadiq Khan, who has been frequently criticised by Mr Trump.

More than 10,000 pounds ($18,400) was raised via a crowdfunding site to get the six-metre inflatable up in the air — smashing the original target of $9,000.

The balloon was designed to have a "menacing face" and "tiny hands". ( Reuters: Peter Nicholls )

Mr Trump will spend Friday meeting the Queen at the Sandhurst military academy outside London and holding talks with Prime Minister Theresa May at her Chequers country home before heading to Scotland.

Tens of thousands of protesters are expected to demonstrate against his visit in London.

Mr Trump, who arrived in Britain last night, told The Sun newspaper that the planned protests in London and other British cities made him feel unwelcome, so he was avoiding the capital as much as possible.

The Trump Baby balloon is six-metres high. ( AP: Matt Dunham )

"I guess when they put out blimps to make me feel unwelcome, no reason for me to go to London," Mr Trump told the newspaper.

"I used to love London as a city. I haven't been there in a long time.

"But when they make you feel unwelcome, why would I stay there?"

The "Trump Baby" balloon has become quite the spectacle in London. ( Reuters: Peter Nicholls )

ABC/wires