At the moment of the explosion there was a brilliant flash of light, ten seconds later an enormous roar sounded and a fearful blast swept across the area. Sharp rays of heat emitted massive amounts of radiation all over Nagasaki within seconds and because there were no barriers to the spread of radiation huge amounts of Nagasaki, were destroyed almost instantaneously.
Click on the photos below to enlarge:
The destruction of the Fat Man as shown in this painting
People didn't feel anything abnormal, as this radiation didn't produce sound or heat but in actuality it had permeated deep into their bodies and affecting them greatly. The temperature directly under the explosion was estimated to be somewhere from 3,000 to 4,000 degrees Celsius. The force of the blast and the heat rays unleashed immediate destructive power and then fires broke out which severely damaged one third of the buildings in the city with all buildings inside a 2 kilometer radius of the explosion burnt to ashes.
Above are a coupe of images that i took from the Nagasaki Peace Park Museum that shows the full destructive powers of the Nagasaki Fat Man Atomic Bomb and its course of destruction.
Please check out the Nagasaki Fat Man Atomic Bomb at the Nagasaki Peace Park Museum here on a map: