Below is all of the footage I have found so far from the Terrorist attacks in Manchester:
From CNN, You can see the explosion:
People evacuating building:
[youtube https://www.youtube.com/watch?v=D6oBg1vVQZo]
Outside moments after the explosion:
[youtube https://www.youtube.com/watch?v=DUIlRLRzDkw]
More footage:
[youtube https://www.youtube.com/watch?v=JxSMSCYJsis]