I was over at Big-Boys.com and they have a video which they claim is a home made firework. It is filmed in what seems like a highway underpass. It looks like there might be train tracks running between the explosion and the camera. Someone lights a fuse and then runs off camera. The fuse takes awhile to get it done and the explosion doesn't happen until near the end of the video. As you can see in the picture it makes a pretty big boom and mushroom cloud of smoke. Someone in the Big-boys.com comments section posted the following,

Im a pyromaniac/pyrotechnician an in my expert opinion, that was not a bomb or firework. they got that effect by taking a big jug of gas and putting a fuse in it. the "mushroom cloud" effect was caused by the fact that the lid was loose, so all the burnt gas jetted out of the hole really fast.

The voices in the video aren't speaking English so it is a pretty good bet the video is taken somewhere in Europe. Crazy stuff. All that smoke probably brought the fire engines in a hurry.

Check out the video for yourself.