Volunteers were expected to take hours to distribute the works
Teams of helpers left 1,000 works by urban artist Adam Neate around London for people to pick up.
They began their mission as soon as it went dark on Friday afternoon, starting in the outer boroughs and working their way towards the centre.
A spokeswoman for the project said the teams, which worked in all 32 London boroughs and the City of London, would continue into the early hours.
Each piece features a different combination of printing and stamping.
The spokeswoman said the first teams of distributors had begun on Friday afternoon by leaving art in southern boroughs of London, including Bromley, Bexley and Merton.
Neate, whose pieces have fetched up to £43,000 at auction, told BBC News on Friday afternoon that he first left his paintings in the street "years ago, without telling anybody".
I like the idea you can stumble across art in any environment, not just a gallery - you can walk along the street and find a painting
"But I thought, for this one event where I was going to do the whole city in one go, I'd warn people or tell them that this was the image I'm going to be leaving, if you like it you can go out and have a look for it," he said.
"If you don't like it, you can stay at home."
He added: "I like the idea you can stumble across art in any environment, not just a gallery - you can walk along the street and find a painting."
Helpers left the art in areas including doorways and in front of shop windows.
Neate's two and three dimensional paintings use recycled cardboard boxes as canvases and have been noted for their complex layering and bold use of paint.