Nintendo stock is experiencing a sudden rise today. At one point, the stock managed to reach 9.7% above yesterday's level.

So what's up? Bloomberg explains that, among the reasons causing the spike, investors have learned that Nintendo will host some sort of 3DS related event on September 13.

Nintendo hasn't made any mention of a September event, so it's unclear what the investors are referring to. The Tokyo Game Show will be held from September 15 through September 18, but Nintendo, as usual, is not expected to participate. Perhaps Nintendo has something else planned just ahead of the show?