Khan described the blimp as a "peaceful protest."
Trump said he would try to avoid the crowd in the capital during his four-day visit to the country.
"I used to love London as a city," Trump said. "I haven't been there in a long time. But when they make you feel unwelcome, why would I stay there?"
An activist group was given permission to fly the blimp over London during Trump's visit, which will reportedly be met with up to 200,000 protestors in the streets. The group launched a crowdfunding project and has since raised over $40,400.
"Donald Trump is a big, angry baby with a fragile ego and tiny hands," the group's crowdfunding page said. "He's also racist demagogue who is a danger to women, immigrants and minorities and a mortal threat to world peace and the very future of life on earth."
"Moral outrage is water off a duck's back to Trump," the group added. "But he really seems to hate it when people make fun of him."
Trump's visit spurred other activists to create their own political displays. One artist carved "F--- Trump" into a crop circle that was reportedly visible on Trump's flight path to British Prime Minister Theresa May's country estate. SHARE THIS STORY USING ANY OF THE BUTTON BELOW ⬇ PLACE YOUR TEXT ADVERT BELOW ⬇⬇⬇