People have been sending flowers and cards to mourn the sudden death of a doctor at a Beijing hospital, who was allegedly stabbed by a patient's relative.

Early Tuesday morning, the doctor, Yang Wen, was working in the emergency ward at Civil Aviation General Hospital in Beijing when she was attacked by a man who appeared upset over what he perceived as inadequate treatment of his 95-year-old mother.

Graphic surveillance footage shows the man approach Yang from behind as she was seated behind a counter and then say something to her before taking out a knife and cutting her throat.

The doctor was pronounced dead within 24 hours. Sun Wenbin, 55, was arrested by the Beijing People's Procuratorate on Friday.

Hospital security guards and janitors helped people place flowers in a corner on the first floor of the emergency ward. There were more than 200 bouquets of flowers by Sunday afternoon with attached cards paying tribute to Yang, according to one hospital security guard, who wanted to remain anonymous.

The hospital has increased security measures after the incident, and only one family member can now accompany hospitalized patients, he said.

The cards were mostly anonymous, with words wishing Yang peace in heaven. One card read: "I am a doctor from the Inner Mongolia autonomous region. I heard about what happened to you and felt very shocked and angry. Doctors are responsible for saving people's lives. We are not supposed to be the victims. The person who killed you should be punished to the fullest extent."

There were also cards sent by Yang's former patients who thanked her for curing them and praised her for her professionalism and patience.

A patient in her 80s, surnamed Wang, visited the first floor to mourn Yang's death.

"Doctors at the hospital are very nice. What's wrong with the man? Is he crazy? Does he have no heart? He will face karma," she said.

She then turned to the front desk staff and told them to take care of themselves. "Please tell the hospital dean to install security equipment to ensure the safety of doctors and patients."

There will always be violent and even crazy people, and there must be safety measures to prevent them from destroying the lives of good people, she said.

Sun Yang, who lives in Beijing's Haidian district, brought his 10-year-old son to the hospital on Sunday to pay their respects.

"I want my son to know that life is not always full of sunshine and rainbows and bad things can happen to good people," Sun said. "However, people will remember good people for their good deeds and they will always live in people's hearts."

One of Yang's colleagues from the emergency ward told China Central Television that when Yang received the 95-year-old patient on Dec 4, the elderly woman was delirious and vomiting and suffering from complications from a lack of blood and oxygen to the brain.

The patient's family refused to let her be examined, asking only that she be hooked up to an IV drip. When the patient's condition did not improve, her family blamed the doctors.

Though the medical team explained to the family that the patient had suffered from complicated infections and heart failure, and that it can take older patients longer to recover, the family repeatedly quarreled with the staff, the colleague said.

"Yang was a very good doctor. All the patients had good things to say about her. She was a mild person and would not quarrel with a patient," the colleague said.