A spokesman for the Shard said: "The wind got up a bit more than we were anticipating.
I think it was seen from a helicopter and people panicked unnecessarily.
Three workmen were still working on the London Bridge Station side of the Shard this afternoon, having come down as far as around the 25th floor. The trio could be seen slowly descending down the side of the glass-sided building, washing the windows as they went.
There were no signs of them being in any difficulty despite blustery conditions around the skyscraper."
Witness Neil Walsh was waiting for a train at nearby London Bridge station when he saw the drama unfold.
The 30-year-old marketing executive from Dartford, Kent, who filmed the incident on his phone, said:
I go through there every day and always have a gawp up at the Shard to see what's happening.
I happened to notice that the window cleaning box was swinging wildly. It was quite erratic...
It was dangling from quite a thin arm and was a few feet away from the building itself, rocking left, right, up and down. It was swinging all over the place. The last few days have been windy and it must have been worse up there.