2,057 smiley-faced clouds floated over Bankside on Wednesday morning as British artist Stuart Semple experimented with a never-before-used technology.
The Happy Cloud installation is intended to be a message of hope and positivity in response to current events.
One happy cloud (helium, soap and vegetable dye) was released every seven seconds between 8am and 12 noon.
"I just wanted to make a piece of work that could cheer people up a bit," said the 28-year-old artist.
"I've had enough of the doom and gloom in the air and I wanted to show something completely positive floating up in the sky."
"This was the most straightforward way I could think of to literally contribute something happy to the atmosphere.
"I am hoping it might put a smile on a few people's faces as they go through their day. I am also keen to help people remember that the success of British cultural industries is relatively new.
"I believe that cultural industries have been hugely important in the rejuvenation of parts of the city and a very wholesome and important contributor to the economy.
"I know at times like this it's easy to make creativity a low priority but I want to show on a very human level that an artistic idea might be able to do something important, even for a fleeting moment."