Anyone who survived the world's first atom bomb blast must have felt the worst was past. But Kazuko Sadamaru was caught up in the second explosion too. That she did so and is still alive today is perhaps the most uniquely improbable story of all.

The road north of Hiroshima, winding through rice paddies and cedar green mountains, leads to the quintessentially Japanese home of Mrs Sadamaru. This unassuming woman, sitting cross-legged and wearing slippers on a tatami mat by the veranda, is among a handful of people alive who witnessed both the Hiroshima bomb and the obliteration of Nagasaki three days later.

'I never wanted to speak out about my experience,' she said, breaking a 60-year silence in an interview with The Observer. 'I haven't published anything or talked to anyone because I didn't want anyone to know. I only became a nurse because I wanted to devote myself to patients and the country. I never dreamt Japan would lose the war. I worked and worked believing Japan would win.

'I cannot forget the events on 6 and 9 August 1945. I saw the flashes and the mushroom clouds of both A-bombs dropped on Hiroshima and Nagasaki. So many were exposed to the A-bomb but I am one of the few people who have experienced the two bombs, and still I am in good health. It was fate that I was there, but I had good luck in that I survived both bombs.'

Sitting near her golden Buddhist shrine and pouring iced green tea, Mrs Sadamaru, now 80, explained that she left her hospital in Nagasaki on 5 August 1945 to accompany a soldier to a town near Hiroshima, some 260 miles away. The following day, she was on a train approaching the city when 'Little Boy' exploded at 8.15am.

'The flash came in an instant,' she recalled. 'I remember thinking what happened? Why? What is it? Then we saw a mushroom cloud from the window. No one had heard of the A-bomb. Nobody imagined such a weapon existed. We all screamed.

'The next day I took a train back to my work and the carriage before mine was full of injured army soldiers. Their clothes were badly burnt and tattered, or they were barely wearing clothes at all. Their skins were bloody and peeling and they had blisters. There was a noise of moans and groans - the scene never goes away. They saw me in a Red Cross nurse's uniform and said, "Please help the injured." But I could do nothing. I had no medical supplies.'

Twenty-year-old Kazuko Yamaguchi, as she then was, reached her work at the Ohmura Naval Hospital in Nagasaki to find herself presumed dead. 'I thought I would get in trouble for being late, but my friends thought I had been killed because it had been reported that the whole of Hiroshima was destroyed. They said, "Oh, you're alive," and started to cry. I cried with relief and was pleased to hear that my colleagues cared for me.'

What happened next would kill another 74,000 people - but Mrs Sadamaru was spared again. 'I saw a flash on the glass. Then a bang came and I saw a black cloud rising into the sky. The flash was just like the one I saw in Hiroshima. When I heard the sound I knew it must be the bomb.

'The first survivors came on a truck. All their clothes were tattered, they were bleeding all over and their skin was burst, swollen or peeled off. Their clothes stuck to the burns, so we used scissors [to cut them off]. They were writhing in agony, especially those who were burnt all over, and some even fell from their beds. I heard helpless voices, crying for water. It was difficult to identify the bodies' ages and gender because even the name tags were burnt.

'We had to keep working all day without rest and I automatically did whatever I had to do. There was no time to think how sorry I was to see so many miserable patients. I tried to comfort them by saying, "Hold on, hold on. I know how hurt you are." For those who had lost their children, I said, "They'll be OK, you'll find them," although I knew I was lying.'

Despite being close to both bombs, she suffered only a temporary abnormal white blood cell count and loss of hair. In 1946 she married Sadato Sadamaru, now 86, and has a son, a daughter and four grandchildren.

The modest Mrs Sadamaru refuses to be photographed, but did permit pictures of her Red Cross cap 'because I'm proud I was a nurse'.