Thursday's drill in Nîmes simulated an emergency response to a so-called dirty bomb explosion, containing toxic properties of chemical substances. The exercise took place among a crowd of football fans watching a match on an outdoor screen.
On Friday video of the mock drill could be seen on YouTube and social media sites.
The drill involved 1,200 students from the Ecole Nationale de Police, plus 480 other participants from other sectors including defence, health and the ministry of the interior.
A spokeswoman for the police academy said it was the biggest training exercise ever carried out in France.
French Interior Minister Bernard Cazeneuve attended the drill, which was organised by police, gendarmerie, soldiers and emergency services. Speaking at the event, Cazeneuve said, "here in Nimes, what we have wanted is to test in particular [a case] that concerns a chemical and bacteriological risk. Not that there is a real risk of this kind of an attack but we must - because the principal of precaution dictates it - envisage all hypotheses."
France remains on high alert following last year's 13 November terror attacks in Paris, which killed 130 people and injured hundreds of others. The UEFA Euro 2016 tournament will be the largest public event to take place in France since those attacks.