As well as the discussion of death, Yao also likes to hear about his patients' lives, such as their happiest memory, or their biggest regret and how they managed to negotiate life's challenges.

Yao has asked these questions to hundreds of his patients and their relatives whose authentic images are recorded in the photos, including the distraught daughter of a patient, a smiling old woman and an elderly man with closed eyes.

"People who are sick have complicated or different facial expressions even though they are all in pain or distress, for example, gentle, upset, proud or defensive," says the 30-year-old doctor.

Yao began taking photographs in college. One of the photographers he admires is Lyu Nan, who lived with patients suffering with mental distress and took photos of, and for, them.

"Lyu inspired me to find art in real life, instead of going somewhere to take photos," says Yao.

The first patient Yao took a photo of was a retired teacher who had lung cancer.

The patient passed away before Yao had a chance to give it to him. He brought the photo to his funeral and presented it to his relatives.

Yao's photos allow him to get closer to the patients and communicate better with them.

"I realized that patients I used to differentiate and identify from their bed number or their disease are unique. Behind each face, there's a story," Yao says.

"The patients in my wards are often aged, and have witnessed historic moments such as the founding of the People's Republic of China, and the reform and opening-up. I'm curious to know their stories."

He recalls there was a patient who told him about the travails and suffering he endured when digging a river bed in the 1950s.

"He said the weather was so cold that the mud was frozen, and they stood in the water barefoot, digging the river for years. Some died and some were disabled," Yao recalls.

All the photos are taken in black and white, as he thinks this better captures the essence of a person.

Some patients decline to have their photos taken but the majority are enthusiastic.

"Photography connects doctors and patients," he says.

"Everyone wants to be heard, and they all have their own stories."

Yao thinks that both medical science and photography provide a care for both the physical and mental aspects of his patients.

"Medical science respects the body, enabling patients to live more decently, while the photography respects people's lives objectively," says Yao.

Yao's father had hepatitis B and Yao was offended by what he viewed as the medical profession's indifference. This pushed him to become a doctor and he vowed to treat his patients with respect and warmth.

His first month as a hospital intern in 2013 had a profound influence and he wrote in his journal in English:"Too many people in need".

Yao often smiles when talking with his patients.

"If a patient offered his or her hand to me because of the pain, I'll hug him or her, hoping to help alleviate both the pain and that feeling of helplessness," he says.

On the other hand, Yao notes, doctors need the trust and understanding of their patients.

Sometimes there is nothing they can do to prolong life. Doctors are not magicians.

As the final journey nears, patients and their families will have to deal with stress and grief.

Doctors are not immune to this, Yao says.

Yao rides his motorbike as a therapy to tackle any feelings of sadness or inadequacy or pressure related to the patients.

"I ride along the seaside, sometimes, for hours," says Yao.