The possibility of Hong Kong being struck by a devastating tsunami is remote. But a risk does exist. Last month's disaster in the Indian Ocean has shown how important it is to be prepared.
What would happen if a tsunami engulfed our crowded city? The report on the last page of this section gives a spine-tingling insight into the likely consequences. It is based on the projections of scientists - and raises some troubling questions. They envisage a huge wall of water crashing into Central and Kowloon, sweeping through the lower floors of tower blocks and flooding tunnels. The airport would be submerged. Tai Po, Sha Tin and Ma On Shan would also be hit.
This is the stuff of a disaster movie. It might seem alarmist to suggest that we need to guard against such an unlikely event. But one look at the scenes of devastation in nations hit by the recent tsunami should be enough to make us think again. That natural disaster had also seemed unlikely - until it happened.
The government assures us that there is no need for concern. It has a plan. And Hong Kong is part of the network which receives alerts from the Pacific Tsunami Warning Centre in Hawaii.
But geologists at the University of Hong Kong have highlighted potential weaknesses in our defences. They point out that the warning centre underestimated the strength of the earthquake which caused the tsunami. It was 32 times more powerful than originally estimated. This could make a crucial difference to Hong Kong's reaction, leading us into a false sense of security. We might mistakenly believe a tsunami is not strong enough to reach our shores.
There are no underwater tsunami sensors between Hong Kong and the Philippines, where such a tsunami would be most likely to originate. These would give a quicker, more accurate warning of its approach. The Observatory says they may not be cost-effective. This may be true. But in the light of the recent tsunami, serious consideration should be given to whether such sensors are needed.
