London’s ‘Trump Baby’ balloon flies as protests take off in Britain.

The "Trump Baby" blimp, a helium-filled effigy of U.S. President Donald Trump, lifts off from Parliament Square in London on Friday. The "Trump Baby" blimp, a helium-filled effigy of U.S. President Donald Trump, lifts off from Parliament Square in London on Friday. Photo: Bloomberg Photo By Luke MacGregor. Photo: Bloomberg Photo By Luke MacGregor. Image 1 of / 54 Caption Close London’s ‘Trump Baby’ balloon flies as protests take off in Britain. 1 / 54 Back to Gallery

LONDON — The most anticipated installment of Britain’s “Stop Trump” protests — a giant orange balloon of President Trump depicted as a pouting baby in a diaper and holding a smartphone — took flight Friday from Parliament Square in London.

As if they were waiting for a rocket launch, dozens of people — including activists, tourists, children and bystanders taking time out from their commutes — gathered around the 19-foot balloon and counted down from 10 before it was released into the air.

“This is a victory,” said Leo Murray, an activist and the creator of the balloon. “People love it, he hates it, and it’s driven him out of London.”

Murray and other activists behind the inflatable “Trump Baby” have called the balloon a “symbol of resistance,” aimed at sending Trump a clear message that he is not welcome in Britain.

“The only way to get through to him is to get down to his level and talk in a language he understands — one of personal insults,” Murray has said.

“He mocks and insults anyone who doesn’t support him,” said Adam Cottrell, one of the activists behind the balloon protest, “so now he can see what it feels like.”

Not everyone was enthusiastic about the balloon. Lucy Lawson, an American expatriate, came to see it because it was close to her work, but while she opposes Trump’s policies, she said the protest was childish.

“Why are people going down to his level? Why are they being so childish?” she said. “It’s because of his childlike leadership that we are in this mess.”

Lawson asked one of the organizers why they had launched the balloon when they knew Trump would not be in London.

“It’s going to swamp his Twitter feed,” Cottrell said. “There’s no way he doesn’t see this.”

Tens of thousands of demonstrators gathered for a national rally in parts of London beginning at 2 p.m. to protest Trump’s policies. Oxford Street, famous for its shops, transformed into a carnival of slogans against Trump.

“Dump Trump,” “Child Snatcher” and “Trump Special Relationship: Say No,” some of the placards read.

“Hey, ho, Donald Trump has got to go” thousands of people chanted to the beat of carnival drums.

“Trump is the reason that the whole world order is in disarray,” said Peggy Hudson, 37, a doctoral student. “America used to lead the world, now it’s sending us all down the drain.”

Trump spent the night at Winfield House, the American ambassador’s residence in London, where protesters said they had aimed to keep him awake by banging pots and pans and playing recordings of crying children separated from their parents at the Mexican border.

On Saturday, Trump supporters planned to march from the U.S. Embassy in London to Whitehall, where government offices are concentrated. Far-right groups planned to rally, too.

Ceylan Yeginsu is a New York Times writer.