It was a day that the Granville community in western Sydney would never forget.

As the packed train headed from Mount Victoria in the Blue Mountains toward Sydney, hundreds of passengers sat inside the carriages, chatting, laughing, reading newspapers and looking out the windows.

There was no reason to suspect something was wrong.

On this day in 1977, about 8.10am, the locomotive derailed as it approached Granville station, striking one of the steel-and-concrete pillars that was supporting a bridge carrying Bold Street over the railway cutting.

The derailed engine and first two carriages passed the bridge.

But they weren’t out of the clear.

The first carriage broke free from the others and collided with a severed mast beside the track, killing eight passengers.

A train travelling from the Blue Mountains to Sydney Central derailed and a bridge collapsed on top. Photo: Flickr/Blue Mountains Library

The remaining carriages came to a halt a short distance after the second carriage, which remained intact.

The rear half of the third carriage, and forward half of the fourth carriage came to rest under the weakened bridge.

For the passengers inside, their location couldn’t have been worse.

The bridge above them was estimated to weigh about 570 tonnes, and all of its supporting structures had been demolished.

Within seconds, the bridge and several cars on top of it crashed onto the carriages, crushing them and the passengers inside.

Karen Varsanis’s brother died in the Granville train disaster at age 23. Photo: AAP

Half of the passengers in the third and fourth carriages were killed instantly.

Other passengers were trapped in the train for hours after the accident, several with agonising injuries.

#DayoftheRoses Prayers with families & friends of the victims of the terrible Granville Train disaster that occurred 40 yrs ago today pic.twitter.com/qUXvQJ2x56

— NMGSports (@NMGSports) January 17, 2017

At first, some were conscious and able to talk to rescuers, but died shortly after of crush syndrome when the bridge’s weight was removed from their bodies.

Family and friends of survivors and those involved in the rescue efforts gathered on January 18, 2007, to throw 83 roses off the bridge at Granville train station. Photo: AAP

Of the hundreds of passengers on the train, 83 people died and more than 213 were injured.

In 2017, an unborn baby was added to the fatality list as the 84th victim.

Granville train station in 2017. Photo: Getty

The crash, which investigators blamed on poor fastening of the track, made headlines around the world and remains the worst rail disaster in Australian history.

It was responsible for the greatest loss of life in a confined area post-war.

To this day, dozens of emergency services workers and survivors still suffer mentally from memories of the bloody scene.