It was an early spring day in April, but director An Zhanjun felt as if it was the middle of a chilly winter when he scaled the Kunlun Mountains to visit police officers who guard a section of the Qinghai-Tibet Railway, the highest in the world.

At the police station, located on a site where the elevation reaches more than 4,000 meters above sea level, the filmmaker found the person he was looking for.

It was Yang Fuxiang, a stoic brigade leader who, for 13 years, has endured loneliness and extreme weather while manning his post on the snow-capped mountains.

In 2017, Yang was honored as one of the 10 most loyal police officers as part of an annual selection by the Chinese People's Armed Police Force.

His wife, who lost a leg in a car crash, but still selflessly supports her husband by painstakingly taking care of the family, was also awarded by the force.

"Most people may feel uncomfortable and suffer shortness of breath after just spending a short time at an altitude surpassing 4,000 meters. It's hard to believe, and I found it admirable that Yang has stayed there for so many years," says the director, in an interview with China Daily.

"You see very few creatures at such a high altitude. When the officers teasingly told me that there are only two seasons on the mountain-winter and 'a winter-like season'-I could not laugh out but I just felt very touched," he adds.

Recently at the Great Hall of the People in Beijing, alongside his actors, An attended the opening ceremony of his new film, Warriors of Honor, recalling his interviews with the police heroes who inspired it.

The movie, which won the Golden Angel award at the annual 15th China American Film Festival held in Los Angeles in November, debuted in China on Dec 5.

An says it was a senior officer who suggested he should shoot a movie about police heroes, many of whom have tear-jerking stories.