The Halifax Explosion is the name given to the explosion that occurred at 9:05am on December 6th, 1917, in Halifax, Nova Scotia, when two ships, one carrying munitions, collided in the city's harbour. This was the largest ever man-made explosion, until the detonation of Atomic bombs on Hiroshima in 1945. 
On this morning, Norwegian ship Imo, on its way to New York to pick up relief supplies for war-torn Belgium, and going faster than it should've, as well as passing to the left of oncoming ships, rather than the customary right, met the French Mont-Blanc, which was carrying explosives for the First World War. After a series of miscommunications between the two ships, the Imo struck the Mont-Blanc on the starboard bow. This generated sparks, lighting benzol on the Mont-Blanc's deck, which seeped into the holds, causing a fire that raged for 20 minutes. Citizens stared out their windows at the black smoke rising into the air, and firefighters tried to put the fire out.
Vincent Coleman, an rail dispatcher, was one of the few who realized an explosion was imminent after being warned by a Navy officer. He stayed at his post, managing incoming and outgoing rail traffic, and contacting officials, warning them to stop any trains coming in. Among them was the 8:55 A.M. train from Saint John, New Brunswick, which carried hundreds of passengers. Coleman's message to the train, minutes before his death, was:
"Hold up the train. Ammunition ship afire in harbour making for Pier 6 and will explode. Guess this will be my last message. Goodbye boys."
The explosion caused both fires and a tsunami, levelling 2.5 square kilometres of northern Halifax. The blast shattered windows 100 km away in Truro, and could be heard as far as Prince Edward Island. Of the 50 000 population, nearly 2000 died and 9000 were injured. Property damage was estimated to be $35 million.
- "Halifax Explosion," The Canadian Encyclopedia, http://thecanadianencyclopedia.ca/en/article/halifax-explosion/