The time delay between the arrival of seismic waves and tsunami waves that is the basis of the tsunami warning system does not exist close to the earthquake source. Close to the source region itself the source earthquake acts as a warning since it is generally felt by the local population: the problem then, largely solved in Japan and the USA through public education programmes and in regions particularly prone to tsunamis, such as eastern Indonesia, by bitter experience, is to ensure that the people who feel the earthquake know what to do, which is to immediately leave for the safety of high ground. Emergency planning at country or State level, involving the identification and designation with signs of evacuation routes and ensuring that these are not likely to be blocked by the effects of the earthquake, is also of assistance in reducing losses in such areas. A more fundamental problem involves coasts around 500 km to 1000 km from the edge of the earthquake rupture zone, where the source earthquake is unlikely to be felt but the tsunami will arrive less than an hour after its generation. Several states operate the practice of converting a tsunami watch (instituted on the basis of the seismic data alone) into a tsunami warning immediately after large earthquakes close to their shores. This same problem will apply to the whole of smaller areas such as the Caribbean or Mediterranean in which similar systems might be put in place in future.