Pride Park was evacuated due to a flare ahead of Derby’s Championship clash with Cardiff on Friday night.
A flare is understood to have been let off in the concourse of the away end of the ground approximately 30 minutes before kick-off of the match live on Sky Sports.
The players were forced to leave the field during their warm-up and fans congregated outside before eventually being allowed back into the stadium.
An emergency announcement could be heard: “Attention please. This is an emergency. Please leave the stadium via the nearest available exit.