SHENYANG, July 7 (Xinhua) -- An archive in northeast China's Liaoning Province has released footage showing Japanese invaders looting natural resources in China during World War II.

The seven-minute black-and-white film, preserved at the archive of the Anshan City, shows Chinese workers forced to work in iron ore and coal mines, and the resources being delivered to a steel plant built by Japan in Anshan City in 1937.

The film also shows Japanese economic activities in other parts of Liaoning, including Shenyang, Fushun and Benxi.

Ma Lianming, a researcher with the archive, said the footage, shot by the Japanese, was used to promote militarism back home and mobilize more Japanese people to join in the invasion of northeast China.

"Previous knowledge about Japan's plundering of resources in northeast China mostly came from written documents. The rare film, shot by Japanese, is an incontestable evidence of Japan's invasion of China and is of great historical value," he said.

According to records of the archive, Japanese invaders stole more than 10 million tonnes of iron and steel resources from Anshan between 1918 and 1945.

The film was unveiled Thursday ahead of 81st anniversary of Lugou Bridge incident.

On July 7, 1937, Japanese troops attacked the Lugou Bridge, also known as Marco Polo Bridge, on the outskirts of Beijing, triggering China's full-scale resistance against the invasion.