Labour Party leader Jeremy Corbyn, who declined an invitation to Monday's royal banquet for the president, was due to address the protest.
The second day of Trump's state visit will be filled with more official business than ceremony, he meets with May and business leaders to discuss trade and other matters.
"We're sending a very clear message of solidarity to those affected by his despicable politics - and saying loud and clear that the USA president doesn't deserve the red carpet treatment", said Ajuub Faraji, one of the organisers of the blimp.
Large protests are expected during the USA president's visit, as was the case during his trip past year.
Noah continued: "That's like someone being like, 'Haha, this guy has less money than Jeff Bezos!' Yeah, that's all of us!"
"A lot of it is fake news, I hate to say", Trump said. "Khan had said it would be "un-British" to roll out the red carpet for Donald Trump".
May will give Trump a copy of one of the most significant documents in the transatlantic "special relationship" - a framed copy of Winston Churchill's personal draft of the 1941 Atlantic Charter, which defined the Allied goals post-World War II.
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He stressed that many conflicts in the world could be resolved only by combined efforts of the United States and Europe. Pompeo said he hoped that Germany would "follow Britain's example" and ban Hezbollah.
"Let's do this deal", Mr Trump said.
Pregnant protester Lauren Donaldson, 31, who was wearing a t-shirt saying "bumps against Trump" over her baby bump, said she was on the streets because the president's "policies are bad. but he, himself, he's horrible".
Norwegian student Helen Thuen, 25, said of Trump's reaction to the protests: "It's hard to tell with that guy, he might take it as flattery even".
The president teased Mrs May about not suing the European Union during the Brexit talks. "I'm against his ideology", said Hada Morena as she arrived at the palace with a sign that read; "Love the good American people".
Trump said in his toast that the liberation of millions from tyranny in World War II "forever sealed" the bond between Britain and the United States.
"As the UK makes preparations to exit the European Union, the United States is committed to a phenomenal trade deal between the U.S. and the UK", Trump said. Invoking the meme of a man who denied a woman a room in the Holiday Inn Express, Noah mocked Trump in the Queen's voice: "I'm sorry Donald, it's above me now ..."
May has been dogged by her failure to achieve Brexit and is stepping down this week as head of her Conservative Party but will remain as prime minister until her successor is chosen.
Trump has been met with protests this week as well, including the return of a giant blimp depicting him as an orange-skinned baby. The official said if Trump asks aides to arrange a meeting, it would likely occur during a period of downtime on Tuesday afternoon before a formal dinner hosted at the United States ambassador's residence, where Trump is staying. Huawei denies it is, or could be, a vehicle for Chinese intelligence. Trump will turn from pageantry to policy on Tuesday as he joins British Prime Minister Theresa May for a day of talks likely to highlight fresh uncertainty in the allies' storied relationship.