Director Zhang Yimou has generous words of praise for Christian Bale, who leads the cast of his latest war epic, Heroes of Nanking.

He says Bale arrived on the set in Nanjing (formerly known as Nanking), a city in East China, alone on Feb 2 and insisted on the same accommodation as the crew.

"In my 20-year filming career I have never seen this - a Hollywood A-lister coming alone to an alien country and living with a crew of hundreds of foreigners," Zhang was quoted as saying in a statement put out by his production company. "That's very impressive to me."

In the film Bale plays an American priest who helps a group of sex workers and female students trapped in a church during the Nanjing Massacre of 1937, in which Japanese troops killed 300,000 Chinese civilians and soldiers.

Bale is supported by a number of Chinese actors such as Dou Xiao, leading man in Zhang's last film Under the Hawthorn Tree, but Zhang has kept the identities of the actresses playing the sex workers and students, under wraps.

Bale's professionalism made a deep impression on Zhang. According to the contract he was expected to work for 12 hours a day at most, but when Zhang wanted to shoot overtime, the actor accepted without hesitation, the statement says.

"When I needed a certain type of performance he gave me three approaches, and when I needed three approaches he gave me five," Zhang says. "He always provided more than enough choices."

Producer Zhang Weiping says he found it incredible that Bale would make an unusual request to cut his lines.

"Most actors try to have more lines, but Bale was more keen on the accuracy and appropriateness of his lines. When he found his lines were too wordy, he asked that they be cut down," he says.

The Oscar-winner for The Fighter also surprised the crew because of his friendliness and by attending the birthday party of an extra.

Bale completed his part and left for Britain recently. After a short break he will join Christopher Nolan's new episode of the Batman film series.

Zhang's crew is now working on the war scenes, enhanced by the team of Joss Williams, the special effects supervisor of The Pacific and Band of Brothers.

Heroes of Nanking is Zhang's third film after directing the widely acclaimed Opening Ceremony of the 2008 Beijing Olympics. The $90 million film, an attempt by Zhang to create a Chinese Saving Private Ryan, is expected to be released on Dec 16.