More than 700 security personnel and 1,200 police cadets took part on Thursday in a simulated chemical attack on a football match as part of security preparations ahead of the 2016 Euro Championships to take place in France in June and July.
Interior Minister Bernard Cazeneuve said as he arrived for the exercise that it would help "ensure that this great sporting festival takes place in conditions of maximum security".
Around 1,000 police cadets posing as football spectators were massed in a mock fan zone for the drill at the National Police School in the southern city of Nimes.
Suddenly, a massive explosion rocked the area and a cloud of gas rose into the air, sowing panic as the actors tried to flee to safety.
In the streets, rescue workers wearing gas masks and hazmat suits tended to actors posing as the injured and contaminated.
It was the first of several such drills planned in the run-up to the competition in the wake of last November's jihadist attacks in Paris that killed 130 people.
One of the attacks took place at the Stade de France stadium in Paris as France were playing Germany in a football match, though the three suicide bombers were unable to enter the venue and only one person was killed outside.
The Stade de France will host the final of Euro 2016 on July 10th.
Three southern host cities - Marseille, Nice and Toulouse - will have fan zones for people to watch matches on giant screens outside the stadiums.