This happened at ORPT this weekend. This is VERY scary stuff. That is a blind corner. From what I have gathered (you can see it in one of the video's) is an exhaust came off a bike (don't know which) and started a chain reaction.
Here is another video, you can actually see just how high the guys bike went in this video.
Here is another video of that session. Around the 10:50 mark you can see the flags are waiving already and you can see the exhaust on the track. I think this could have been avoided if people were paying more attention to the flags.