In the narrows of Halifax harbour, a Norwegian ship and a French freighter carrying some two and a half thousand tonnes of high explosive for the war in Europe collided at low speed. The French ship caught fire and drifted burning against a pier while people came to the windows to watch. Twenty minutes later she detonated. About two thousand people were killed and nine thousand injured, a square kilometre and a half of the city was flattened, and the blast was heard more than two hundred kilometres away. The wave of glass from the windows blinded or damaged the eyes of hundreds who had been watching, which led to advances in the treatment of eye injuries and in care for the newly blind.

A blizzard arrived the next day. Boston sent a relief train within hours, and the medical teams it carried arrived while the city was still burning; Nova Scotia has sent Boston a Christmas tree every year since, which stands on the Common. Vince Coleman, a railway dispatcher, stayed at his key to warn an incoming passenger train and was killed by the blast; his message survives. The memorial bell tower stands on the hill above the district that was destroyed.