Godstog 50325 Trecate-Gricignano) fremført af et litra E655 lokomotiv (E 655 175) med 14 bogietankvogne (den forreste vogn var registreret som tilhørende PKP, de andre 13 vogne registreret hos DB) afsporedes i Viareggio kort før midnat lokal tid (22:00 UTC) den 29. juni 2009. De afsporede vogne ramte huse langs jernbane.

Toget var udgået fra Trecate og skulle til Gricignano di Aversa. En vogn afsporedes og yderligere tre vogne afsporedes som følge heraf. Vognene der ejedes af KVG Kesselwagen, en division af GATX og udlejet til ExxonMobil og ERG (ejerne af det olieraffinaderi vognene kom fra), varwere reported to have been carrying Liquefied Petroleum Gas (LPG).[10] Two of these exploded and caught fire.[6] Seven people were reported to have been killed when a house collapsed.[6] An eighth person who was killed was reported to have been riding a scooter on a road adjoining the railway.[10] A child was found carbonised in a car in front of the house where he lived with his parents. It is speculated that his parents put him in the car to save him and then returned to the house to save other two children.

The two members of the train crew suffered minor injuries in the accident. A large area of Viareggio was damaged in the subsequent fires caused by the wagons carrying LPG exploding.[6] Twenty-six people were reported to have been injured in the accident.[2] The accident is the worst rail accident in Italy since the collision between two trains in Murazze di Vado near Bologna on 15 April 1978, which killed 48 people.[12] It was reported that a whole street had been destroyed in the explosion and fire

A state of emergency was declared by local authorities.[14] Around 1,000 residents of Viareggio were evacuated from their homes as a result of the accident.[8] Italian Prime Minister Silvio Berlusconi visited Viareggio „to take control of the situation“. His visit was not well received, with boos and cries of „go home“.[15] Dr Enrico Petri, an eyewitness and local hospital physician, said that 36 people had been taken to Versilia Hospital in Viareggio suffering from 80-90% burns. He compared the aftermath to a terrorist attack.[13] The accident left around 100 people homeless.[14] The accident resulted in the disruption of rail services between Rome and Genoa.[15] Viarregio railway station was partially reopened on 3 July 2009.[16]

Ferrovie dello Stato (FS) has opened an investigation into the cause of the accident.[17] Italian police said that the accident may have been caused by damaged tracks or a problem with the brakes on the train.[6] Italian union CGIL is reported to have blamed the decrepit state of the rolling stock,[15] but the maintenance of the wagon was a responsibility of GATX [18] The failure of an axle on the wagon that derailed is being investigated as a possible cause.[14][19] Italian Transport Minister Altero Matteoli informed the Italian Parliament on 1 July that a defective axle may have caused the accident.[16]