Emergency services were sent to the Shard today - days before its official opening - after a window cleaner got stuck in a precarious position on the 72nd floor.
Ten firefighters attended the scene in central London this afternoon after reports of the cleaner's cradle on the outside of the building becoming unsafe.
A video posted on YouTube appeared to show the cradle swinging in the wind at the top of the tower, which has 78 occupiable levels.
On-site engineers fixed the problem. An ambulance was on standby at the bottom of the 309.6 metre (1,015ft) high building but the window cleaner was not thought to be injured.
London Fire Brigade, which sent a fire engine and fire rescue unit to the Shard, said in a message on Twitter: "On site engineers at the £Shard have made the window cleaner's cradle safe & we can all now breathe a sigh of relief."
The Shard, which is the tallest building in Western Europe and has 31.4 acres of space, will be officially opened by Sheikh Hamad Bin Jassim Bin Jabor Al Thani, Qatar's prime minister and minister of foreign affairs, and the Duke of York on Thursday.
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, which is what drew my attention to it.
"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.
"I filmed it thinking the box was empty. That was a worry in itself, without me realising there was someone inside, probably cowering in a corner and hanging on for dear life."
A spokesman for the Shard said: "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.
"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.