Aberfan clock that stopped at the moment of the disaster goes on display in museum

9:13. The precise moment the coal tip hit the village of Aberfan and the precise moment the clock stopped.

It was 21st October 1966. Just as children were starting school a coal tip high on a nearby mountain came crashing down engulfing Pantglas Junior School and nearby houses.

116 children and 28 adults were killed.

Nobody can be sure where the clock came from. Did it belong to a teacher at Pantglass? Perhaps it was an alarm clock used in one of the demolished homes.

What is known is that a rescuer, Mike Flynn recovered the clock and preserved it for decades. The clock still retains some of the coal slurry that killed so many.

Today, his son, also called Mike, handed it over to the National Museum at St Fagans where it will be permanently kept and put on display.

• The Aberfan disaster: What happened that day?

The school day had not long started when, witnesses later said, there was an ominous rumble in the distance.

A massive coal tip - a mountain of waste generated by the town's mines that employed 8,000 people - had collapsed, sending thousands of tonnes of slurry sliding into the village.

The avalanche of slurry buried the school and engulfed the 240 pupils and staff inside.

There were 11 tips in the hills overlooking Aberfan. The one that collapsed was Tip Number 7; standing more than 111ft high, it was begun in 1958 and was estimated to contain 140,000 cubic yards of waste.

The mountain of spoil sat on underground springs; weeks of heavy rainfall had saturated the ground making the spoil heap unstable.

Members of the morning mining shift clocking on at 7.30am on 21 October after another night of heavy rain noticed there had some slippage in Number 7 tip.

At 9.15am, a swathe of Tip Number 7 broke away and began sliding down the hill towards the village.