Vehicles burned inside the St. Gotthard tunnel near its southern end at Airolo, Switzerland. At least 10 people died and 10 were injured when two trucks collided head-on, starting the fire.

One of the trucks was carrying insulation material and the other was loaded with tires, which helped fuel clouds of smoke, according to police.

Eight victims were in cars not involved in the crash, but were overcome by smoke.  

(New York Times, October 25 2001)