Players, fans and members of the media were forced to evacuate Derby County's Pride Park shortly before the Championship fixture against Cardiff City on Friday night.
Wales Online have reported that the evacuation - which happened at 7.15pm - was due to flares being set off in the away end.
An announcement came over the tannoy, with the message saying: "Attention please, this is an emergency. Please leave the stadium by the nearest available exit."
Fire exits around the ground were all opened up, with fans and media streaming out onto the car parks around the ground.
The evacuation only lasted a short amount of time, before everyone was allowed back into the stadium.
Kick-off wasn't delayed, with the match - which is being broadcast live on Sky Sports - still getting under way at 7.45pm GMT.
Mirror Sport's James Nursey, who is at the match, tweeted: "Working at Derby v Cardiff tonight. Stadium is being evacuated after an “emergency” announcement. Hopefully a false alarm but no word why."
He then followed that up by tweeting "Everyone allowed back in! Panic over , no explanation" just a few minutes later.
The meeting of Phillip Cocu's Rams and Neil Warnock's Bluebirds is the first in the second tier following the international break.
Warnock was critical of staging the game on Friday, with many of his players having been away with their countries over the past week.
“Leandro Bacuna is not even flying back until this afternoon,” he said on Thursday, via Derbyshire Live.
“It’s scandalous really how countries can get away with things like that.
“I know we have got to do it for television because of the finance but Friday night after an international break doesn’t help us when they are going all over the world."
