For modern Chinese students it is not the Great Famine but the Three Years of Difficulties. The catastrophe remains so sensitive that their history books do not document how many starved to death, or why. Yet more than 50 years ago, at the height of the disaster, a handful of their predecessors published an underground magazine bluntly accusing Communist leaders of causing the devastation. "The dead couldn't tell," said one of the authors, Xiang Chengjian. "I decided to sacrifice myself … I was ready to die."

The story of Spark, and the boldness of the students, is the latest piece of China's past unearthed by film-maker Hu Jie. His documentaries have traced the Maoist excesses of the 1950s, 1960s and 1970s, and the extraordinary individuals who swam against the tide.

"I want people to have a chance to get to know real history," he said. The bearded former soldier, still muscled in his mid-50s, was fired from the state news agency Xinhua after he began working privately on his first film,entitled Searching for Lin Zhao's Soul. Lin was a youthful, gifted dissident executed as a counter-revolutionary, who had written defiant letters in her own blood while in jail.

Soon after came two startling documentaries about the cultural revolution. Though I Am Gone records the brutal death of teacher Bian Zhongyun at her pupils' hands; My Mother Wang Peiying is about the execution of a woman who called on Mao Zedong to resign.

The subjects Hu tackles are so sensitive that some of those involved have not discussed them even with their families. He has persuaded a remarkable range of witnesses to go on camera; some are grateful for the chance to talk after years of suppressing the truth.

"I'm trying to save all of this material. If these people die, the memories are gone," Hu said.

But some simply refuse to talk, and one of the interviews in Spark stops abruptly when the interviewee receives a phone call warning him not to speak. Such challenges help to explain why the film was five years in the making.

"I don't start with a preconception of these films," Hu said. "It's a discovery process for me. I've always known there's something there, but not quite what it was. In the process of making these films I find out.

"I knew there was a publication, but didn't know what it was about; I just knew people died for it."

The Great Famine was caused by Mao's adoption in 1958 of the Great Leap Forward – an attempt to send industrial and agricultural production soaring by means of collectivisation and revolutionary zeal.

Local officials, through ambition and fear, grossly overstated their harvests; food desperately needed in the countryside was shipped to the cities and even overseas. Cadres harassed, beat, detained and killed those who tried to alert higher authorities, stole food to survive or sought to flee the famine.

As they watched the corpses pile up, a small group of students decided to act. The two issues of Spark – all they produced before they were caught – said that communes had turned farmers into slaves, and railed against the cadres who feasted while the people starved.

"Chinese intellectuals remained silent. No one dared to criticise the government," said Hu. "Only the students dared to speak out, at the cost of their lives."

Hu is not alone in his work; others in China have sought to document the catastrophe. Yang Jisheng, a former Xinhua reporter, spent 15 years working through official archives to produce his account, Tombstone. Another film-maker, Wu Wenguang, enlisted young people to gather oral histories. But none of this work can be released in China, and Yang has come under fire recently from deniers who refuse to accept that tens of millions died or that the Great Leap Forward was responsible.

"These people in the documentaries were dying for us – they sacrificed themselves to save us. We are indebted morally to tell their stories," said Hu.

At one stage, he shot wedding videos to fund his documentaries; now he and his wife, Jiang Fenfen, rely on their pensions. They work on a shoestring budget, buying standing tickets for trains and bedding down in the cheapest hotels. "My sacrifice personally is not worth mentioning, but I admire my wife's contribution," he said.

He is slowing down as he ages, and spending more time on his earlier love, painting – though his works are often inspired by themes related to his films. But he hopes a new generation of documentary makers will realise the importance of the era and take on the task he has shouldered.

"If you don't go to record it, maybe nobody will," he warned.