Organised by Yazmany Arboleda, a 31-year-old conceptual artist from the United States, the project was an unusual attempt to bring a dose of creativity and fun to a city wrecked by decades of war.
The timing of the event, which had been kept secret, came just hours after Taliban militants launched a major suicide and gun attack on a compound of the International Organisation for Migration (IOM) in central Kabul.
"I did think of calling it off last night but all the volunteers insisted it continued," Arboleda said. "I could hear explosions from my house but everyone was just ignoring them and doing the last-minute preparations unaffected."
"They said that this is what happens in their city, and they have to get on with their lives. How people have embraced this shows how much creativity, positivity and love there is here despite everything."
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At distribution points in the city centre beginning at 07:00 am, adults were given one balloon each and encouraged to keep them until the end of the day.
Arboleda, who is based in New York, has arranged similar balloon projects in Nairobi in Kenya, Bangalore in India and Yamaguchi in Japan.
The continuing threat in Kabul was underlined when a suicide bomber killed himself in his house in the south of the city this morning when he was preparing explosives, police said.