United Nations Radio

Although it took hours in most cases for the tidal waves to reach the affected countries, authorities were unaware that tidal waves or tsunamis were headed their way.

As a result, they say they were largely unprepared and did not take any precautionary measures since there was no official alert system in the region.
John Harding is Programme Officer of the International Strategy for Disaster Reduction in Geneva.  He says these type of events do not occur very often, particularly in the Indian Ocean:

"The reason why the early warning system didn't work is principally because the Indian Ocean and the countries around the Indian Ocean do not have an effective early warning system for Tsunamis in the same way the Pacific Ocean has."

The tsunami warning centre is located in Hawaii.