A window cleaner was stranded 72 floors up when high winds buffeted the Shard skyscraper.
A passerby filmed a cradle swinging at the top of the 1,015ft skyscraper, without realising there was a person inside.
The London Fire Brigade was called to the scene along with an ambulance, but building engineers were able to make the cradle safe before they arrived.
A spokesman for the Shard confirmed that a window cleaner was in the cradle as it was thrown from left to right.
"The wind got up a bit more than we were anticipating and the window cleaner was brought down to ground level. He wasn't hurt."
The safety of the window cleaner was confirmed by Mace, the main contractor working on the site. The company said in a statement: "We can confirm that the wind speeds were well within safe limits and that the building maintenance unit was operating in the right way.
"Nobody was injured and the operatives were able to resume work."
Footage of the swinging cradle was posted by witness Neil Walsh, 30, a marketing executive from Dartford Kent. He said he filmed the cradle believing it was empty and posed a danger to people on the ground.
"That was a worry in itself, without me realising there was someone inside, probably cowering in a corner and hanging on for dear life," he added.
Although the window cleaner, who was not identified, was safe, there can be little doubt that turbulence at that height would be a terrifying experience.