Their ambulance has an inbuilt negative-pressure chamber, allowing air in but not out. This prevents cross infection and the possibility of spreading the virus.

Wen always sits beside the patient and uses life support equipment to ensure that the patient's condition does not deteriorate on the way to hospital.

"The transfer of critically-ill patients can be a very dangerous task. But I can't show any panic or fear. I need to make the patients feel reassured," says Wen.

Once they put on disposable protective clothing, they wear it for four to five hours and then disinfect the vehicle. They drink little water to avoid visiting the bathroom.

Wen, who started working at the department in 2002, still remembers the fight against SARS, or the severe acute respiratory syndrome, in 2003.

"In those days, the older doctors volunteered to take on the heaviest tasks. I am an older one now. I should also take the initiative," he says.