'Trump baby' blimp takes to the sky as mass protests of US president begin in London
WATCH: Bigger protests are planned for Tuesday, as organizers and Scotland Yard are bracing for 250,000-plus anti-Trump protesters.

The infamous "Trump Baby" blimp was seen flying across London on Tuesday as protesters turned out in the thousands during the U.S. president's state visit.

Thousands were scheduled to attend the protest on Tuesday, beginning in London's historic Trafalgar Square at 11 a.m. local time. More than 9,000 people registered to attend the protest on its Facebook page, with another 33,000 posting they were interested in attending "Together Against Trump -- stop the state visit."

Anti-Trump demonstrators inflate a giant balloon depicting US President Donald Trump as an orange baby in Parliament Square in London on June 4, 2019.

The "Trump Baby" blimp, a giant balloon that depicts the president in diapers holding an iPhone, will serve as the focal point of the protests just a year after it dominated headlines during the president's last visit to the U.K.

A large robot depicting President Donald Trump on the toilet using a smartphone is another eye-catching feature of Tuesday's protests.

A spokesperson from "Together Against Trump" told ABC News that the group expects protests to take place throughout the country, but that the event in Trafalgar Square is the main event.

A number of Facebook groups, including the "Stop Trump Coalition" and "Stand up to Trump," have organized protests against his state visit so that the "world will know that people here reject him and his toxic politics."

"On 4 June thousands of protesters will be marching to surround Trump as he joins Theresa May on a visit most believe should never have happened," a spokesperson for "Stand up to Trump" told ABC News. "We will be bringing central London to a standstill. By the time he leaves he will know, and the world will know, that people here reject him and his toxic politics."

Socialist Jeremy Corbyn, leader of the Labour Party, the U.K.'s second largest, also spoke to protesters in London Tuesday. In an interview with the Sunday Times last week, Trump warned that Corbyn, who could be the next prime minister, is "making a mistake" if he refuses to treat the United States as an ally.

Protesters hold placards as they gather in Trafalgar Square during a demonstration against the State Visit of President Donald Trump in central London on June 4, 2019.

Corbyn said that the protests of Trump were an opportunity to "stand in solidarity with those he's attacked in America, around the world and in our own country" on Twitter.

Corbyn also referenced Trump's criticism of London Mayor Sadiq Khan, whom the president described as a "loser" just before arriving in the U.K.

During his speech, Corbyn spoke to protesters about Brexit and climate change and told protesters London was a place of ethnic and religious diversity that should be celebrated.

Leader of the Labour Party, Jeremy Corbyn, heads to address protesters outside the Houses of Parliament on the second day of U.S. President Donald Trump's State Visit on June 4, 2019 in London.

"We are the living embodiment of what a democratic society should be," Corbyn told protesters in London. "I'm very disappointed, particularly today, on the wonderful festival of Eid, that our wonderful mayor of London Sadiq Khan has been attacked in the way that he has. Racism divides, the exploitation of minorities divides … and brings about a horrible place to live in."

"@SadiqKhan, who by all accounts has done a terrible job as Mayor of London, has been foolishly "nasty" to the visiting President of the United States, by far the most important ally of the United Kingdom," the president said in a tweet Monday. "He is a stone cold loser who should focus on crime in London, not me."

Trump was responding to criticism from Khan in an article for the Observer, in which the mayor said that it was "un-British to roll out the red carpet for Donald Trump."

Demonstrators protest against the visit of President Donald Trump in London on June 4, 2019, on the second day of Trump's three-day State Visit to the U.K.

London's Metropolitan Police said they would be undertaking a "multi-faceted security operation" to deal with the protests, which are expected to be peaceful.

"Protestors will not be marching past Downing Street at any point," the police said in a statement. "This is a multi-faceted security operation, and whilst the Met has a responsibility to ensure the right to peaceful protest, this needs to be balanced with the complex requirements of this policing plan."

"We are anticipating a number of additional protests to take place across central London" during Trump's visit, police added.