Nanking, a new, U.S.-made documentary based on the historical bestseller The Rape of Nanking, opened in Beijing on Tuesday.

Based on the book by the late U.S. author Iris Chang, the 90-minute film recounts the horrific atrocities committed by Japanese troops against the citizens of the Chinese city — now known as Nanjing — about a year prior to the start of the Second World War.

Producer Ted Leonsis, vice-chair of online powerhouse AOL, personally financed the approximately $2 million US film after reading Chang's book, which includes eyewitness accounts of the carnage and tells the stories of an unlikely group — a doctor, a U.S. missionary and a Nazi businessman — who collaborated to set up a safe zone for the Chinese.

"At a time when Americans are not well-liked around the world, the story of many Americans helping the Chinese could help," said Leonsis, according to trade publication Hollywood Reporter.

Leonsis, who has compared Nanking to Steven Spielberg's Holocaust film Schindler's List, also said he wants those of Chinese descent to watch it "by any means necessary," including viewing unauthorized versions available on the internet or on pirated DVDs.

Many people in the Western world "don't know this movie but they should," said the film's co-director, Bill Guttentag.

"This is a film about the best and worst of humanity."

Nanking, which will open more widely across mainland China on Saturday, is one of several new film projects about the Nanjing massacre set for release this year — the 70th anniversary of Japan's full-scale invasion of China before the Second World War.

Set in 1937, the film combines grainy images of Nanjing's destroyed buildings and landscape — littered with the bodies of men, women and children — with accounts of rape and torture told from the perspective of victims, witnesses and even the soldiers themselves.

Woody Harrelson, who reportedly worked for free, and Mariel Hemingway are among the Hollywood actors who read diary entries that were penned by Westerners living in Nanjing at the time.

The film was among the audience favourites at the 2007 Hot Docs Canadian International Documentary Film Festival and an award winner at Sundance.

Controversy continues

Over the years, the Chinese and Japanese governments have butted heads over acknowledgement of the actions of Japanese soldiers on the Chinese mainland in the 1930s through to the end of the Second World War.

In recent years, conservative lawmakers in Japan have caused an uproar by accusing China of exaggerating stories about the Japanese army's wartime brutality and inflating the number of people killed in Nanjing in 1937. Some have even alleged that the massacre was a fabrication.

Historians generally say that Japanese soldiers killed approximately 150,000 citizens in Nanjing and raped tens of thousands of women. Chinese officials put the number killed at 300,000, while some Japanese put the death toll at 20,000.