Staff at a hotel near Euston station were left in "complete shock" when a man who had been fatally stabbed collapsed in the lobby.
Eleven people are being held on suspicion of murder in connection with the attack.
The victim died at the scene in Euston Street, Camden, on Monday night after coming in from the street.
The "four or five" staff working near the lobby at the time are "trying to come to terms with it", he added.
Laura Collings, 34, a guest who was on a business trip from Manchester, said she returned to the hotel shortly after the man's body had been taken away.
There were "quite a few people walking around looking upset" who seemed like "they might have been associated in some way" with the victim, she said.
Police were called to the scene at about 10.45pm, and the man was pronounced dead about 45 minutes later.