The two trains had started from different points in Messinia — from Kyparissia — and converged at Patras before continuing northeast toward Athens. Train 304 was a regional service, stopping at every station. Train 306 was an express, stopping only at major stops. The faster train closed the gap between them steadily as both ran along the same single-track line. After 304 paused at Derveni station to take on passengers, it moved a short distance beyond the platform and then stopped again. The reason has never been firmly established. Contemporary press speculation offered multiple accounts: a sailor fainted and a panicked woman pulled the distress signal; an elderly woman fainted; a pregnant woman, overcome by the heat and crowding, caused a passenger to reach for the emergency handle. Fifty-six years later, the exact cause remains unknown. What is certain is that one crew member walked back down the track and placed a warning signal behind the stationary train. It was not enough.

Train 306, running at approximately 80 kilometres per hour, passed through Derveni station without stopping. The warning signal went unseen. By the time the drivers of 306 spotted train 304 stopped on the line ahead, they had no room to brake. At 6:50 in the evening, the engine of train 306 struck the last carriage of train 304. That carriage was reduced, as the Peloponnisos newspaper reported at the time, to a shapeless mass of metal. Three more carriages derailed. The passengers who survived but were injured called out for help. The bang was heard in the village of Derveni, and residents came running to the scene.

Soldiers from the School of Engineering at Loutraki, police officers, and nurses were among the first responders. Thirty-four people died. More than 150 were injured. The Peloponnisos newspaper also reported — at the time — that the express train was being handled by a driver who had only just qualified, and that the four crew members had been engaged in conversation as the train ran through Derveni, which is how the warning signal was missed. Whether those reports were accurate, the investigation under a military government was constrained by the political context. There was no independent press, no freedom of inquiry. The disaster occurred the day after a referendum that the junta had organised to legitimise its own rule — the trains were full precisely because the regime had required citizens to vote in their home towns, filling carriages with returning passengers. The collision happened in a country where grief was not freely expressible and accountability was not freely sought.

The Corinth rail disaster held the grim distinction of being Greece's worst railway accident at the time it occurred. It was surpassed in 2023 when two trains collided near Larissa in the Tempi valley, killing 57 people — a crash that sparked nationwide protests over railway safety and the years of neglect that had made it possible. The disaster at Derveni is remembered now primarily through regional journalism and commemorative pieces rather than national memorials. The 34 people who died on 30 September 1968 were ordinary passengers: voters going home after an obligatory exercise in a country that was not free, on a train they had no reason to fear. They deserve to be remembered as individuals, not as a statistic from an inconvenient political moment.