A documentary film on the lives of 22 sex slaves in China who survived World War II has become an unlikely hit.

Su Beiqi, the head of the film's promotional team, said they expected the low-budget documentary, Twenty Two, which was shown on just 1 percent of China's 45,000 screens on its opening day Monday, which was international "comfort women" day, to have fewer screens as time passed.

But the unexpected enthusiasm shown by viewers has changed the plans.