Broadcaster John Humphrys was a young reporter when he was sent to cover the Aberfan disaster of 21 October, 1966. The tip slide onto the south Wales village left 116 children and 28 adults dead.
He told BBC Wales reporter Melanie Doel how he remembers events unfolding on that day.
MD How were you alerted to the story and what was your initial reaction to being sent on such a story?
JH I was sitting in the newsroom at what used to be called Television Wales and West (TWW). We got a bit of wire service copy coming in saying there had been a tip slide at Merthyr Vale and a school had been affected.
To be honest I didn't think much of it because that sort of thing was happening all the time in the Welsh valleys. It was a quiet news morning and I knew the area well so I jumped in the Mini and drove up.
There were lots of people women standing on their front door steps sort of looking up the valley - you just got the sense, I felt, and I said so at the time, that something big had happened.
Of course I didn't know what it was. We didn't even know whether anybody had been killed at that stage, but you could feel it.
MD When you got there, can you describe the scene that met you?
JH I didn't recognise Aberfan. I knew Merthyr Vale and Aberfan very well. I'd worked in Merthyr for years. I had one of my closest friends living in Merthyr Vale. His father worked in the pit and I had stayed in his house many times, which looked over the school.
When I drove down, as far as it was possible to drive into Aberfan, I didn't know where I was. I simply could not reconcile what I was seeing with what I remembered.
The tip slide hit the school from behind
There was just this great mass of muck and filth and utter chaos, and it was terribly, terribly difficult to make any sense of it at all. I think partly one's brain refuses to recognise what one's eyes were seeing.
MD You got very close to parents in your reporting. How difficult was it to see them digging for their own children?
JH You saw the men digging, lots of them stripped to the waist. The knowledge that they were digging for their own children was indescribably awful.
They'd rushed up from the coal face obviously the moment they heard what happened. Their faces were still covered in coal dust and there were streaks of white running down their faces - sweat, and tears. It was ghastly beyond belief.
Every so often somebody would shout for silence because they thought they heard the sound of a child crying out. Everybody stopped digging the moment they said that. There was absolute silence and you all stood there waiting.
Mercifully sometimes it was the cry of a child and they were able to dig down. Some children were brought out alive - but too many weren't.
MD How difficult was it to remain detached - was there a time you thought, 'I can't do this, I just want to help and become part of the rescue'?
JH No, I don't think I ever felt [that]. These men knew what they were doing. They were skilled miners and it would have been presumptuous and very silly to want to get involved.
But of course one felt a part of it, just as a human being, whether you lived in that community and knew these people or not. I had lived there and did know them. I drunk many evenings away in the club at Merthyr Vale and Aberfan.
What was important, as the days and months went by, was the world knew what happened and more importantly why it happened, because it didn't need to have happened.
The miners were the best people to attempt the rescue effort
In spite of the lies we were told at the time, warnings had been given. The men who were looking after that tip knew that there were dangers, and they were not listened to.
That was an utter disgrace - which shamed the whole National Coal Board then and does to this day .We should all hang our heads in shame as a result of that.
As time went by, we realised the enormity in every sense of what had happened, and the disgraceful way in which the authorities had behaved.
MD Did it change the way we treated news? Was this the first time we'd seen human suffering as close up as this?
JH I'm not sure I'd go as far as that. There is nothing to compare with the death of a child. I had covered and have since covered many more disasters - colliery disasters, where miners have died, and of course that is a great tragedy.
But the fact that it was children just transforms it from being a tragedy into something beyond tragedy.
A single death of a single child is a tragedy beyond comprehension for the people involved. Their lives are changed, destroyed. You can't pretend you ever get over the death of a child.
I had a young baby sister who died. I was too young to realise what was going on but my parents never recovered from it.
The fact there were so many, and I come back to this time and time and time again, the fact it need not have happened - that was the evil, worst tragedy of it.
MD How has Aberfan changed you and your outlook on life?
JH I have been a journalist for getting on for half a century now. I have reported wars and disasters all over the world, many of them involving many, many, many more deaths.
But there has never been anything to compare with Aberfan, partly I suppose because I was a relatively young man. I was in my early 20s and had not been a reporter for long.
If you go off to report a war in a foreign country, you know what you are going to get into and you are prepared for it. I'm afraid it's true that it is different if it's your own people who have died, and again particularly if it's young children.
It meant that from an early age I would never see anything as awful as that again. And although the first hours of that first day were indescribable, what was even worse in one peculiar way was watching them taking the coffins out of the chapel - small coffins.
There's something unbearably poignant about the size of a child's coffin. It just wrenches at you. Whatever has happened to me as a journalist since has not paled into insignificance of course, but I suppose I have been able to put things into context.
I have always said and I will always say that nothing - nothing - I will ever see will compare to the horrors of that day.