Pride Park was evacuated 30 minutes before kick off prior to the Championship clash between Derby and Cardiff.
Teams, fans and media were all shown towards the exits after a security alert.
Sky Sports are reporting that the decision was made after flares were found on the concourse of the away end.
That is thought to have set the fire alarms off, forcing Derby to put the safety of the fans first.
Kick-off still went ahead at 7.45pm after the incident.
Neil Warnock’s side already faced difficult preparations in the build up to the clash.
Lee Tomlin missed out with whiplash after he was involved in a car crash earlier in the week.
It’s been a mixed start for both sides in the second tier of English football.
Cardiff have won two games, drawn two and lost two, leaving them on eight points.
Derby are on a run of five without a win after they opened the season with three points on the road at Huddersfield.
New boss Phillip Cocu is taking his time to adapt to English football after replacing Frank Lampard in the hot-seat, after he returned to Chelsea in the summer.
