A loud bang

Today, when my sister and I were going home after doing the shopping (dragging heavy shopping trolleys behind us), we heard a really loud bang. It was maybe a block away, but we could see all the way to the place the explosion (?) took place, since there was a parking lot and the waterfront/harbour between us and whatever happened. For quite a long time there was a cloud of smoke hanging in the air over the water. I have no idea what it was. I also couldn’t see anyone who might have been responsible. It was a little scary.