Historians say at least 300,000 civilians were slaughtered and tens of thousands of women raped in the Japanese rampage.

Trying to tell the Nanjing story on the big screen has been hard for Hong Kong director Yim Ho and his mainland counterpart Lu Chuan. They have gone through tough vetting by the Chinese government that reflects conflicting agendas of Chinese nationalism and good diplomatic relations with Japan.

Both say they've received governmental approval, but only after an elaborate vetting process that involved multiple departments, despite both having Chinese state-run movie studios as partners.

Yim, a respected art-house director who made the 2001 movie "Pavilion of Women" featuring Willem Dafoe, said his script was first rejected by China's Film Bureau several years ago before getting approval on a second try this year.

Lu, a rising Chinese director, said the approval process for his movie, titled "Nanking Nanking," took five months. Nanjing was known as Nanking by in the West at the time of the massacre.

"The process was more tense than usual. It was more complicated than usual," he said.

In Yim's case, he said his movie was vetted by the Film Bureau, the Chinese foreign ministry and the Chinese Communist Party's Central Propaganda Department.

The Chinese government's careful handling of the two movies are apparently motivated by the desire to promote nationalism and boost the image of the Chinese Communist Party, and to maintain strong ties with economically important Japan on a year that coincides with two sensitive anniversaries.

This year marks both the 70th anniversary of the massacre and the 35th anniversary of Sino-Japanese diplomatic ties.

The Japanese invasion of China helped expose the failures of the then-ruling Nationalist Party, said Phil Deans, a scholar on Sino-Japanese relations at Temple University's Japan campus.

"How can you make that pot simmer without making it boil? That's the delicate balance the party has to do," said Deans, who predicts the new movies may portray the atrocities as being committed by a clique not representative of the Japanese people.

Yim's movie is a $35 million (euro26 million) English-language production with Hollywood investment that the director hopes to craft into a star-studded project.

The Hong Kong director's movie, called "Nanking Xmas 1937," revolves around a group of foreigners who sheltered locals from Japanese brutality.