A 21-year-old man has been arrested on suspicion of trespass after a person was seen climbing The Shard building in central London.
Metropolitan Police officers were called to the 1,017ft-tall (310m) skyscraper at 05:38 BST.
London Fire Brigade and the ambulance service also attended, and a number of cordons were put in place.
Two other men were detained on suspicion of causing public nuisance, the Met said.
Earlier, Adam Lockwood, a man from Manchester known for a series of similar climbing stunts, posted a picture of himself on the top of the Shard on his Facebook page.
