The other is by journalist Yang Jisheng that was published in Chinese in Hong Kong in 2008 in two volumes running to 1,200 pages and reprinted eight times since then. It is banned on the mainland. This is a translation by Stacy Mosher and Guo Jian.

Many consider to be the most authoritative book on the famine. After his graduation from Tsinghua University, Yang worked at the Xinhua News Agency from January 1968 until his retirement in 2001. This gave him a network of friends, contacts and access into the system that no foreigner and very few Chinese can match. Even fewer would be brave enough, as he was, to document one of the biggest taboos of the communist era, in a work of research that took 10 years.

His conclusions are stated starkly in the first paragraph when he explains the reason for the title. "The first is to erect a tombstone for my father, who died of starvation in 1959; the second is to erect a tombstone for the 36 million Chinese who died of starvation; the third is to erect a tombstone for the system that brought about the Great Famine."

The wealth of both books is the documents and the details, the frontline of history. These are difficult to obtain in a country that considers this event off limits. As those who lived through and witnessed the famine die and the archives that describe them are largely closed to outside scrutiny, so the evidence contained in the two books becomes more precious.

"Beginning in the early 1990s, I took advantage of my reporting trips to consult relevant materials and interview people who had survived the famine," Yang explains. "I travelled from the northwest to the southwest, from North China to East China, from Northeast China to South China, consulting archives in more than a dozen provinces and interviewing more than 100 eyewitnesses … I accumulated documents totalling millions of words and 10 notebooks, which helped me gain a relatively comprehensive understanding of the Great Famine."

He details one of the most tragic events, in Xinyang, southeast Henan province, home to 8.5 million people. "People whom I interviewed who personally experienced the Xinyang Incident were virtually unanimous in the assertion that at least one million people died of unnatural causes, including starvation and physical abuse."

He quotes Yu Dehong, a former secretary to the Xinyang commissioner, as saying that, during the famine, Xinyang had more than 500 million kilograms of grain stored in its silos. "Added to that year's harvest of 1.45 billion kilos, some two billion kilos were available. If the reserve grain had been distributed, no-one would have starved.

"The starving people saw storage silos full of grain but no-one attempted to steal it. People sat alongside storage depots waiting for the government to release grain and crying out 'Communist Party, Chairman Mao, save us!' Some people starved to death sitting next to the grain depots."

The deaths were not only from starvation but also from fierce beatings meted out to people suspected of concealing or hoarding grain. Forms of torture included "tearing out hair, cutting off ears, driving bamboo strips into the palms, driving pine needles into the gums, branding the nipples, tearing out pubic hair, penetration of the genitals and being buried alive".

In one village, a teenage girl killed her four-year-old brother and ate him; their parents had died. Cannibalism was widespread in the areas suffering from famine.

Yang's book contains similar accounts in other provinces he visited, with named sources; it is an extraordinary - and irrefutable - wealth of detail. He puts the largest number of unnatural deaths at 9.4 million in Sichuan, an unnatural death rate of 13 per cent, followed by Anhui with 6.33 million, an unnatural death rate of 18.4 per cent.

"In localities where the leading cadres' political attitude most closely matched Mao's, the effect of the famine was felt most harshly," he wrote. The less local officials implemented Mao's policies, the fewer people died. These policies were to increase grain procurement quotas, set up people's communes and produce iron and steel.

For his book, Zhou travelled over four years from 2006 to nine provinces and visited many remote places to interview survivors and read as many official archives as possible. The book contains 119 documents, of which the record of Mao's words at the Shanghai conference in March 1959 is one of the most devastating.

Zhou found it in the archives of the Gansu Provincial Party Committee, listed "Top secret - the following document is to be handed out only to comrades attending the meeting and must be returned after the meeting".

The wealth of his book is also in the details revealed by these official documents. One documents cannibalism in Linxia district in Ningxia: starving people kill members of their own family or exhume them if they are dead and eat them. Many are arrested. Wang Zhizhen, a peasant woman in Chishui county, Guizhou, goes to the cadre of her brigade and asks for food; he refuses. After the death of her six-year-old daughter, she eats her heart and liver.

Zhou quotes from a speech by Liu Shaoqi, then president of China, on May 31, 1961: "In Hunan, people say three-tenths [of the disaster] was natural calamity and seven-tenths was man-made. The problem was caused by unrealistic grain-collecting quotas, unrealistic estimates, unrealistic procurement figures and unrealistic workloads."

These are the words of the second most powerful person in China at that time: he is admitting the responsibility of the government in the clearest terms.