VENICE (Reuters) – A powerful Chinese film on the plight of political prisoners condemned to forced labor camps in the late 1950s wooed critics in Venice on Monday, with some tipping it as a strong contender for the festival's top prize.

"The Ditch" tells the little-known story of some 3,000 people deported for "re-education" to labor camps on the edge of the Gobi desert, in western China, and struggling to survive extreme climate and acute food shortages.

Billed as right-wing enemies by the government for even mildly criticizing the Communist party or simply because of their background, many died of starvation, disease and exhaustion in the ditches that served as dormitories.

Director Wang Bing spent three years tracking down survivors and wardens of the Jiabiangou and Mingshui Camps for the film, a surprise entry in the main competition line-up that was only revealed on Monday.

"For 10, maybe 20 years, independent Chinese cinema has focused above all else on the social problems of the poorest working classes in contemporary China," Bing says in the production notes.

"The Ditch is perhaps the first film to deal directly with contemporary China's political past, talking as it does about the 'Rightists' and what they endured in the re-education camps. It's still a taboo subject."

The film, warmly applauded at a press screening, is unlikely to be released in its home country, where authorities remain sensitive about how such topics are portrayed.

Still, Bing said he hoped the film would be an opportunity for younger Chinese like him -- he was born in 1967 -- to learn about their country's past.

"I wanted to talk about our history, past events that can be criticized because of the way in which the Chinese suffered, and show them so that people can reflect on them," he told reporters, speaking through a translator.

DOCUMENTARY STYLE

Shot like a documentary, The Ditch focuses on the last three months of life in an annexe camp where the 1,500 prisoners who had survived until then were moved in 1960, as drought ravaged the whole of China.

Initially forced to plough 4,000 hectares of barren land in the middle of nowhere, they are later left to waste in underground dormitories as food runs out and many cannot stand on their feet.

Barely 500 people came out of that experience alive when authorities finally decided to send the prisoners back home.

"Everything in the film really happened at the camp. Nothing has been made up or added," says Bing, who used many non-professional actors for his first feature film after a string of documentaries.

The Ditch is one of 24 titles vying for the Venice film festival's top Golden Lion prize which will be awarded on Saturday.

Also in competition and premiering on Monday is "Essential Killing," a different struggle for survival with Vincent Gallo as a suspected Taliban fighter on the run from U.S. forces in Afghanistan and later in Europe.

With very sparse dialogue, and not a single word uttered by its lead character, the film by Polish director Jerzy Skolimowski follows Gallo's escape through a snow-blanketed forest, and also stars Emmanuelle Seigner as the mute woman who briefly helps him.