A man from Beijing stabbed five policemen to death in Shanghai on Tuesday in an attack meant as revenge for an interrogation last year, police sources said.

A doctor in Shanghai's Changzheng Hospital rescue a police officer. [Photo: Shanghai Daily]

The suspect, surnamed Yang, stabbed a security guard at a police branch in the Zhabei district of Shanghai at 9:40 a.m. with a knife and started a fire at the gate of the facility.

He then charged into the building and attacked nine officers with his knife. Five police officers died of their injuries, authorities said.

The injured are being treated in three hospitals in Shanghai. One of them is in a critical condition.

"When the four of them were carried into the emergency room, their bodies were soaked with blood and their faces were pale," said a witness surnamed Jia in the Shanghai Changzheng Hospital.

"The scene was too horrible to watch," he said.

One policemen named Fang Fuxin, 47, died before reaching the hospital and Zhang Jianping, 48, after two hours of treatment.

Both died of traumatic hemorrhagic shock in the lower right lung, according to doctors with the hospital.

The other two, both in their thirties, were stable and recovering from head and chest wounds.

Yang, 28, was apprehended by police at the scene and detained.

He was unemployed and from Beijing. He allegedly told police he had been interrogated in October last year by police in the branch who suspected he had stolen bicycles. He was unhappy about the interrogation and wanted revenge.

On Tuesday afternoon, the police building was cordoned off. Criminal investigators were collecting evidence at the scene.

"I saw two people in police uniform carried out from the office at around 10 a.m., one clearly with his stomach cut open" said a female witness surnamed Chen, who worked in a Christine's Bakery near the Zhabei Police Office.

"They were followed by another two injured policemen, one hurt in the head and another in the shoulder. Their clothing was soaked with blood," she added.

Chen said she saw another policeman in blood-stained clothing carried out later.

"He was bandaged and one foot was shoeless," she said.

Wu Zhiming, a senior official of the Shanghai municipal Committee of the Communist Party of China, and Zhang Xuebing, director of the Shanghai public security bureau, were supervising the investigation.