Impressive explosion filmed in Gaza

A video shows a huge explosion filmed somewhere in the Gaza Strip. A vast, ring-shaped cloud is seen spreading rapidly. Even if we go forward frame by frame, no bombs or missiles can be seen falling just before impact. This suggests that explosives may have been placed underground, perhaps in a tunnel. The explosion comes abruptly around the thirteenth second of the video. We don't know the exact origin of the event, but the images have caused quite a stir online.