The former child actor appeared at the annual event to promote his new movie Kill Your Darlings and his presence at the city's picturesque Lido caused devotees to scream and hyperventilate.
Radcliffe had to be surrounded by a team of bodyguards and police as he was guided into the Lido to conduct a press conference, but the media chat was disrupted as fans thumped on the walls and rattled the windows in an attempt to get closer to their idol.
Speaking to reporters at the event, the 24 year old admitted he was a little overwhelmed by the crazy response from the public, but said, "Thankfully, it's not always like this. I've been dealing with it in various ways since I was 11. I don't take it seriously, actually I think it's funny."