The Sino-UK documentary Earth: One Amazing Day features 38 wild species from 22 countries, including white-headed langurs in China. [Photo provided to China Daily]

But the biggest surprise for him and his colleagues was the white-headed langur, an endangered animal that lives in South China's Guangxi Zhuang autonomous region.

They are rarely known outside, he says.

"They are such lovely monkeys. They come down to the forest to feed during the day, but in the evening－just like us－they are afraid of the dark. They are worried about things that might come and eat them."

The monkeys climb back into their caves in the cliffs when night falls.

To film their movements, the crew flew around 200 drones over the area, some carrying long-lens cameras to keep distance from the monkeys so as not to frighten them.

Another interesting moment came during the filming of pandas.

Fan says the photographers wore costumes with panda excreta to "cheat" the cubs, which otherwise would have gone far away from the cameras.