My Love, Don't Cross That River documents the daily lives of an elderly Korean couple who were married for 76 years. [Photo provided to China Daily]

South Korea's My Love, Don't Cross That River opened the documentary section of the ongoing Beijing International Film Festival on Sunday.

Released in 2014, the film, which has been shown at more than 40 such festivals around the world, made its China debut at the sixth edition of the weeklong Beijing film festival that began last weekend.

Jin Mo-young, the film's 46-year-old director, comes across as someone who pays little attention to his appearance, and his documentary that shines a light on South Korea's aging society, speaks for itself.

He got the idea of shooting the film from a Korean TV program that featured Jo Byeong-man, then 98, and his wife, Kang Kye-yeol, 89.

Until Jo's death in 2013, the couple had been married for 76 years, and Jin decided to follow them around for some 15 months in Hoengseong county, Gangwon province, to explore the "secret" of their love by documenting their daily activities.

"I never expected it to be such a big hit," Jin tells China Daily.

"In South Korea if a documentary attracts 10,000 viewers to the cinema, it has already done well."

So far, his film remains the top-grossing documentary in South Korea, with more than 5 million domestic viewers in a genre still considered niche in many parts of the world.

Jin says he minimized his intervention in the film, allowing scenes to narrate the couple's story, because neither the husband nor the wife looked camera-shy.