It will go down as one of the most inspiring survival stories ever to emerge from a horrific war. Tsutomu Yamaguchi was in his twenties when he found himself in Hiroshima on the morning of 6 August 1945, as a single B-29 US bomber droned overhead. The “Little Boy” bomb that it dropped from its payload would kill or injure 160,000 people by the day’s end.

Among them was the young engineer – who was in town on a business trip for Mitsubishi Heavy Industries – who stepped off a tram as the bomb exploded.

Despite being 3km (just under two miles) from Ground Zero, the blast temporarily blinded him, destroyed his left eardrum and inflicted horrific burns over much of the top half of his body. The following morning, he braved another dose of radiation as he ventured into Hiroshima city centre, determined to catch a train home, away from the nightmare.

But home for Mr Yamaguchi was Nagasaki, where two days later the “Fat Man” bomb was dropped, killing 70,000 people and creating a city where, in the words of its mayor, “not even the sound of insects could be heard”. In a bitter twist of fate, Yamaguchi was again 3km from the centre of the second explosion. In fact, he was in the office explaining to his boss how he had almost been killed days before, when suddenly the same white light filled the room. “I thought the mushroom cloud had followed me from Hiroshima,” Mr Yamaguchi said.

His is a truly remarkable story, all the more so because, for years, its protagonist was determined to play it down. But now, at the age of 93 and dying from cancer – probably caused by the atomic bombs that almost killed him, twice – Mr Yamaguchi has finally been awarded the recognition his life deserves. This week, the Nagasaki and Hiroshima governments recorded Mr Yamaguchi as a double-hibakusha, acknowledging that he was exposed to both blasts that incinerated the cities in 1945. “As far as we know, it is the first time that a dual exposure to atomic bombings has been entered into an A-bomb survivor’s ID,” officials said.

Living out his final days in the rebuilt Nagasaki, where he resides with his daughter, Toshiko, the old man is happy his tale is reaching people around the world. “After I die, I want the next generation of hibakusha and the children after that to know what happened to us,” he told The Independent in a telephone interview.

Like many of the roughly 260,000 survivors of the atomic explosions, Mr Yamaguchi suffered agony for much of his life, as his daughter explains. “Until I was about 12, he was wrapped in bandages for his skin wounds, and he went completely bald,” says Toshiko, now 60. “My mother was also soaked in black rain [the famously radioactive rain that fell after both bombings] and was poisoned. We think she passed on that poison to us.”

Yamaguchi’s children, like many second-generation hibakusha, have also been plagued by health problems. His son, Katsutoshi, died of cancer in 2005 aged 59. His daughter Naoko has, in Toshiko’s words, been “sickly” all her life. His wife died last year, aged 88, of kidney and liver cancer after a lifetime of illness. “I suffer too from a terribly low white blood cell count, so I worry about what will happen to me,” Toshiko adds.

But his children’s illnesses aside, Mr Yamaguchi seemed determined to live his life as normally as possible. After recovering from his burns and radiation sickness, he returned to work as a ship engineer in the local port, and rarely discussed what happened to him. “Afterwards he was fine – we hardly noticed he was a survivor,” recalls Toshiko. Her father raised his family and declined to play any part in the anti-bomb activities that fill the lives of some survivors because “he was so healthy, he thought it would have been unfair to people who were really sick”.

Mr Yamaguchi must have watched the world outside his city with alarm. Six decades after his horrific experiences, the US alone has 8,000 active or operational warheads, each carrying on average about 20 times the destructive power of Hiroshima. The once-select nuclear club of America, Russia, China, France and Britain has been swelled by new recruits Israel, Pakistan, India and probably North Korea. Even conservative Japanese politicians hint that they might one day need the bomb.

“I can’t understand why the world cannot understand the agony of the nuclear bombs,” he says, speaking through his daughter. “How can they keep developing these weapons?”

Along with thousands of others, Mr Yamaguchi applied for hibakusha status with Nagasaki when the government finally began to provide health assistance (and later other benefits) in 1957. His government-issued ID stated he was exposed to radiation only in Nagasaki, thereby neglecting his unique status as a double survivor. And he saw no need to draw attention to it.

But as he got older, things changed. In his eighties, he finally wrote a book about his experiences, and was invited to take part in a documentary called Nijuuhibaku (Twice Bombed, Twice Survived), about the handful of double A-bomb victims. The film shows him weeping bitterly as he describes watching bloated corpses floating in the city’s rivers and encountering the walking dead of Hiroshima, whose melting flesh hung like “giant gloves”.

Three years ago, the film was screened at the UN in New York, where Mr Yamaguchi, by then wheelchair-bound, pleaded with the audience to fight for the abolition of nuclear weapons. “As a double atomic bomb survivor I experienced the bomb twice, and I sincerely hope that there will not be a third,” he said.

His friends, including local journalist Masami Miyashita, told him he should make his status official. “I’ve never met anyone like him,” says Mr Miyashita. “There are other people who suffered in both bombings, but nobody I know who was so close to the blasts. To survive once is agony; twice is a miracle. But he has never made a big deal about it.”

Today, Mr Yamaguchi believes that God “planted a path” for him. “It was my destiny that I experienced this twice and I am still alive to convey what happened,” he said. So in January this year, he filed a request for double recognition.

Very late in life then, and much to his surprise, the retired engineer finds himself making a small piece of history, and seeing his face in newspapers and on TV across the world. Some have called Mr Yamaguchi the luckiest man alive, but his daughter says he rarely considers such things. “He laughs when asked why he was so lucky,” says Toshiko. “He just doesn’t know.”