The balloon flew on the second day of Trump's three-day State Visit to the UK

A giant inflatable blimp depicting Donald Trump as a sneering baby in a diaper flew outside the British parliament in London on Tuesday ahead of what is expected to be one of the city's largest protests against a foreign leader.

The six-metre high blimp was raised in Parliament Square at 0900 GMT. It is due to be airborne when Trump holds talks with the outgoing British Prime Minister Theresa May nearby in Downing Street.

Trump and his wife Melania arrived on Monday for a three-day state visit - a pomp-laden affair that involved a banquet at Buckingham Palace on Monday evening.

Leo Murray, 42, the co-creator of the blimp, said: "We're trying to remind the president how unwelcome he is in this country.

"We're also, in a light-hearted way, trying to articulate the strength of feeling against Donald Trump and his politics of hate," he said. "We want to put a smile on people's faces as well as make a serious point."

Around 100 activists counted down from 10 to one for the launch of the blimp, which was first used during Trump's visit to London last year. It was tethered a few meters off the ground.

The launch marked what is expected to be a day of protests across the country. In central London the leader of Britain's opposition Labour Party will join tens of thousands in a "Carnival of Resistance" against the president.

Jeremy Corbyn, who will speak at the rally after snubbing Monday night's banquet at Buckingham Palace, said it was an "opportunity to stand in solidarity with those he's attacked in America, around the world and in our own country".

Among those taking part will be environmental activists, anti-racism campaigners and women's rights protesters.

Police will close the road directly outside Downing Street to protect the president and his family.

In Britain, Trump's ban on travel to the United States from several primarily Muslim countries, the decision to withdraw the United States from a global deal to combat climate change, and his criticism of British politicians have helped stoke opposition to his presidency.

The state dinner held in the president's honour was boycotted by several lawmakers, including the leader of Britain's Liberal Democrat party as well as Corbyn and other senior Labour figures.

The U.S. president's supporters said it was an insult to snub the leader of Britain's closest ally. But the demonstrators have received tactical support from Mayor of London Sadiq Khan, who has repeatedly clashed with the president and who gave permission to fly the blimp.

Trump called the mayor a "stone-cold loser" shortly before he arrived in Britain and has in the past accused him of failing to do enough to stop deadly terror attacks in London.

POMP AND PROTESTS

Trump said he is "loved" in Britain despite the protests. He said he was closer to Britain than any other American leader, citing his mother's Scottish roots and the two golf courses he owns in the country.

"Tremendous crowds of well wishers and people that love our country," Trump said in a tweet on Monday.

"Haven't seen any protests yet, but I'm sure the Fake News will be working hard to find them. Great love all around."

The first day of Trump's visit was taken up with royal engagements and ceremonies. The focus switches to business and politics on Tuesday.

There was a heavy police presence in Whitehall, the centre of Britain's government, on Tuesday, with metal barriers and concrete blocks used to close the southern part of the street.

Protesters from all over Britain have travelled to London to join the demonstrations. Other protests against Trump's visit are planned in 14 cities and towns.

Trump's last visit in July cost police more than 14.2 million pounds ($17.95 million). At the time, 10,000 officers were deployed from all over Britain.

London's Metropolitan police said 2,591 officers were deployed on Monday for the visit.

Scott Lucas, a professor of international and American studies at the University of Birmingham, said other U.S. presidents such as Ronald Reagan and George W. Bush have faced large protests in Britain.

He said the protests typically tend to be larger for American presidents than leaders from other countries such as China or Saudi Arabia because the two countries are historic allies.

"America is our friend and you have to be able to speak to your friends in a certain way," he said.

"You are usually more concerned about someone who is in your own household, or your neighbour down the street, than someone who is in the next village or town."