University of Science and Technology student Chow Tsz-lok only had a 15 percent chance of surviving when he reached hospital and it would have made little difference if he'd arrived 10 minutes earlier, a doctor told the coroner's court.

Chow, 22, died from brain injuries four days after he fell from the third to the second floor at Tseung Kwan O's Sheung Tak Estate car park in the early hours of last November 4, while police clashed with anti-government protesters nearby.

Calvin Mak Hoi-kwan, a neurosurgeon from Queen Elizabeth Hospital who operated on Chow, testified before coroner Ko Wai-hung yesterday on the 20th day of the inquest.

Mak's medical report showed that an unconscious Chow was sent to the hospital at 2am on November 4 with severe brain injuries, pneumothorax and bone fracture in his pelvis.

Chow underwent brain surgery at 4am and another one at 3pm, both of which did not alleviate his conditions. Doctors declared Chow dead at 8.09am on November 8 after a failed attempt to save him from a cardiac arrest.

Mak said that based on Chow's first CT scan taken half an hour after he reached the hospital, the probability of him dying within two weeks was 85 percent.

If he did survive, there was over 90 percent chance that he would have become vegetative or remained in a deep coma permanently.

Earlier on Wednesday, senior ambulanceman Cheng Kwun-ming told the court that the ambulance could have arrived where Chow fell 10 minutes sooner if it was not forced to make detours due to the protest scene.

But Mak estimated that Chow's condition would have been similar even if he managed to get to the hospital 10 minutes earlier.

"Normally, it's the sooner, the better for treating brain injuries. But in Chow's case, the chance of death is the same," he added.

Mak said he could not determine whether the student was harmed or unconscious before his fall but believed it is possible that all his injuries were caused by the fall after the coroner explained that it took less than one second for Chow to plunge by 4.3 meters.

Within that second, Chow might not have enough time to react to protect himself even if he was conscious, according to Mak.

Forensic doctor Kwok Ka-kei also testified yesterday, saying she did not find signs of being shot, burnt or assaulted on Chow's body during the autopsy. Nor was there traces of tear gas or pepper spray.

Calvin Mak says Chow Tsz-lok only had a narrow chance of survival. Sing Tao

Court hears Chow had only 15pc chance of survival