10 March 1945: 334 B-29s dropping incendiaries destroy ~267,000 buildings; ~25% of city[8] (Operation Meetinghouse) killing some 100,000
(Source: http://en.wikipedia.org/wiki/Bombing_of_Tokyo)
Some 70,000–80,000 people, or some 30% of the population of Hiroshima, were killed by the blast and resultant firestorm,[102] and another 70,000 injured.[103] Over 90% of the doctors and 93% of the nurses in Hiroshima were killed or injured—most had been in the downtown area which received the greatest damage.[104] Out of some 70,000–80,000 people killed, 20,000 were soldiers.[105] Most elements of the Japanese 2nd General Army were at physical training on the grounds of Hiroshima Castle when the bomb exploded. Barely 900 yards from the explosion's hypocenter, the castle and its residents were vaporized. The bomb also killed 12 American airmen who were imprisoned at the Chugoku Military Police Headquarters located about 1,300 feet (400 meters) from the hypocenter of the blast.[106] All died in less than a second.[107]
(source: http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki)
So nearly as many people killed in less than a second Hiroshima, and an estimated 40,000-75,000 died at Nagasaki in that same amount of time and the main part of the city was protected by a series of hills as the target was an industrial complex in the Urakami valley.