HIROSHIMA: With a blinding flash of light and an ear-splitting roar, the age of nuclear conflict arrived with terrifying and awe-inspiring force on August 6, 1945, changing the course of history, and killing 140,000 people.

The morning was a run-of-the-mill one for most Hiroshima residents.

Housewives made breakfast for their families, children played in the sticky summer heat, and men hurried to get ready for work.

Few could have known the dangers above them as a US B-29 bomber, the Enola Gay pierced the sky, loaded with deadly cargo in its belly, the single most fearsome weapon the world had ever seen.

At 8:15 am, the pilot released Little Boy, a uranium bomb with a destructive force equivalent to 16 kilotons of TNT.

After the initial searing fireball, gusts of around 1.5 kilometres a second roared outwards, carrying with them shattered debris, and packing enough force to rip limbs from bodies.

The air pressure suddenly dropped, crushing those on the ground, and an ominous mushroom cloud rose, towering 16 kilometres above the city.

The smell of burning flesh filled the air as scores of badly injured survivors tried to escape the inferno by diving into the rivers that criss-crossed Hiroshima.

Countless hundreds never emerged, pushed under the surface by the mass of desperate humanity; their charred bodies left bobbing in the brackish water.

Many died of their terrible injuries over the following hours and days; lying where they fell, desperate for help that would never come, or even just for a sip of water.

For those who survived, there was the terrifying unknown of radiation sickness still to come.

Gums bled, teeth fell out, hair came off in clumps; there were cancers, premature births, malformed babies and sudden deaths.

Seven decades later, some stone buildings that survived the supersonic blast still bear the shadows of anything -- or anyone -- that was incinerated in front of them.

The mangled skeleton of a domed exhibition hall -- the only structure left standing near the epicentre -- stands as a grim reminder of the power of the world's first atomic bombing, a sight that Barack Obama will see Friday when he becomes the first sitting US president to visit the city.

The Hiroshima attack was followed three days later by the Nagasaki bombing.

In the wake of the overpowering twin bombs, Japan surrendered less than a week later, ending World War II.