BBC now saying there's a second device that may have been near the train station that's scheduled for a controlled explosion shortly.
Manchester Police also confirming it was a terrorist attack.
I was just coming here to comment that is likely. Just like Boston bombing and Bali bombing, you should always anticipate a second attack. II attack could be another bomb or depending on the location a gunman.
If you've survived the first blast, and you are not immediately next to it rendering Aid to the injured , you should likely shelter-in-place. In a stadium like that you're probably safer Sheltering in the bathroom then you are running into the large concentrated crowd out the front door as is anticipated.
You can die in the Stampede or you can die in a secondary attack.
Sadly, this is the kind of thing we have to think about.