A camera used to record the weather 10 miles from Belper caught the moment of explosion. Four seconds into the video, a column of smoke appears in the middle of the picture.
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Police have been forced to close down motocross event near Sedgefield after one rider was killed and another seriously injured.
A woman hit by police gunfire during a counter-terrorism operation has been arrested after being released from hospital.
Police have been granted extra time to question a man who is being held on suspicion of planning a terror attack.