China's latest blockbuster film, to be released nationwide Thursday, focuses on the hypersensitive topic of famine -- but not the mass starvation that Mao Zedong presided over, which remains strictly taboo.

"Back to 1942" tells of a largely forgotten disaster that left three million dead, seven years before Mao's Communists took over and almost two decades before his Great Leap Forward led to the deaths of tens of millions.

It has drawn wide local attention with Chinese stars Zhang Guoli and Chen Daoming and Hollywood figures Adrien Brody and Tim Robbins among director Feng Xiaogang's cast, and a 210 million yuan ($34 million) budget.

The famine struck the central province of Henan, which had been torn by fighting between Chinese and Japanese forces while also suffering a drought, locust attacks and government mismanagement.

The area was still recovering from deliberate breaches in dams along the Yellow River that caused massive flooding four years previously, in a desperate attempt to check the Japanese advance.

The film is presented as "one of the most sombre moments in recent Chinese history".

Yet neither the filmmaker, actors nor the local press have made any mention of the far larger famine of 1958-62 under the Great Leap Forward, Mao's failed economic overhaul.

Its policies led to the deaths of 40 million people, estimates Chinese journalist Yang Jisheng, who investigated the famine for over a decade for his recent book "Tombstone", which has been banned in China.

"The West only knows the 1962 famine, they don't know about the 1942 famine, so it is necessary to depict it, as a history lesson," Feng said in response to an AFP question during a press conference on Sunday.

But when asked about the possibility of making a similar film about the starvation under Mao, the director did not answer.

"You have to respect the constraints that exist, you know, and how difficult it is for filmmakers," said Brody. "It's remarkable that they are able to make a film like this."

It remains unclear whether China's vigilant censors have allowed the release of "Back to 1942" to distract attention from the later famine, or if the move represents a relaxation of the taboo.

"Whatever the merits of the film, it was probably decided to do it to serve as a counter-argument to Yang Jisheng's book," said Philippe Grangereau, co-author of the documentary "The Great Famine".

It was a typical example of Chinese "counter-propaganda", he said.

According to the Hollywood Reporter, China has delayed the release of the latest James Bond movie "Skyfall", prompting the US paper to speculate the move was to boost ticket sales for "Back to 1942" and another Chinese film.

Mao's disastrous Great Leap Forward was intended to transform China from an agrarian economy into a modern communist society through rapid industrialisation and the collectivisation of farming.

In attempts to meet steel production quotas, farm implements were melted down for scrap while party-directed agricultural experiments drove down yields on communes.