Some wore T-shirts saying, "Make London safe again".
A 29 feet long blimp of Sadiq Khan in a striking yellow bikini has taken to the skies above London's Parliament Square. The campaign organiser Yanny Bruere had organised it in protest after Khan allowed Trump Blimp to take skies during his United Kingdom visit in July.
"Obviously a lot of people feel the same, that Sadiq Khan doesn't represent them and doesn't speak for them and obviously they all want to see Sadiq Khan on a giant blimp as well".
The bikini design of the inflatable pokes fun at his decision to ban adverts on the Tube showing a woman in a similar swimsuit.
The stunt comes after the London mayor defended the flying of a similar blimp depicting Donald Trump over the capital during the USA president's visit to the United Kingdom in July.
The campaign added that any surplus funds would be dedicated to efforts to unseat Khan and "for defending free speech which is constantly under attack".More news: Bears to acquire Raiders pass rusher Khalil Mack
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"I think a certain amount of respect should be afforded to the leader of the free world and the greatest ally the United Kingdom has", he said, according to The Associated Press.
It featured the caption "are you beach body ready?" - which was said to promote an unhealthy body image.
The fundraising page for the balloon said: "In light of the Donald Trump "Baby Trump" balloon being allowed to fly over London during his visit to the United Kingdom, let's get a "baby Khan" one and see if free speech applies to all".
Other early supporters included Katie Hopkins and American anti-Muslim activist Pamela Geller.
Dancers perform as a large balloon depicting London Mayor Sadiq Khan in a yellow bikini floats above a small crowd of demonstrators in Westminster, in central London on September 2018. "He has done a awful job", Trump said in an interview with The Sun in July.