The tower of Guangsheng Temple in Hongdong county, Shanxi province, once housed the precious Buddhist canon, Zhaocheng Jin Tripitaka.[Photo provided to China Daily]

His team visited the Guangsheng Temple and surrounding villages, and filmed interviews with about 20 elderly people with firsthand knowledge about the operation.

He describes the recent expedition as another "rescue mission", since many people relevant to the event have died. The team discovered vestiges in the bases of Buddha statues where the scriptures where hidden, confirming interviewees' recollections.

"We also learned many obscure details about the rescue," he says.

"It was an even greater struggle to counter the Japanese as they swept through the area."

Secret meetings and confidential mailing systems were planned to safely transport the scriptures. Local militias also concealed their whereabouts.

NLC researcher Li Jining says woodblocks for the 7,000 chapters were carved from 1149 to 1181 in today's Yuncheng, Shanxi.

The surviving version was printed in Beijing in the late 13th century on Yuan Dynasty (1271-1368) emperor Kublai Khan's orders.

"It's a miracle of the world's printing history," he says.