Hawai'i County will hold an islandwide tsunami-response exercise Tuesday.

Activities related to the exercise will be most visible to residents in or near tsunami-inundation zones and will begin shortly after 8 a.m., when police, firefighters and other county crews are mobilized, officials said.

The exercise will simulate a tsunami generated by an earthquake in Alaska, which would provide four hours of warning before it actually hits Hawai'i. Officials will activate emergency notification procedures for the public, governmental agencies and organizations such as public utility companies and the American Red Cross.

Police will be assigned to key intersections where traffic would be turned back in the event of an actual tsunami warning. The exercise will be over once police report that all simulated roadblock locations are secure, expected to be by 10 a.m.

Civil Defense will use its new electronic mass emergency notification system, City Watch, in conjunction with the exercise. The automated telephone system quickly notifies large numbers of county personnel to respond to emergencies.

For more information about the exercise, call Civil Defense at 961-8229.