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Civil Defence chiefs have completed an evacuation system to be used if a tsunami strikes Auckland.
A network of 30 sirens around the west coast and the inner reaches of the Waitemata Harbour will be tested for the first time next Sunday.
The sirens are at populated sites in Waitakere City less than 10m above sea level, including much of the Te Atatu Peninsula and large parts of Piha.
Waitakere Mayor Bob Harvey says his council's decision to fund the system is a "prudent measure" to ensure the city is prepared. The maximum predicted height of any tsunami affecting the city is 2m on the west coast and 3m on the east.
"While the risk of a major tsunami affecting Waitakere is small, it cannot be discounted," said the city's Civil Defence manager Bill Morley.
The system will broadcast three signals if a tsunami hits. A dash-dash-dot-dot pattern sounded for 15 minutes will alert people to evacuate beaches, listen to radio and watch TV for information and prepare to leave their homes.
A dot-dot-dot pattern sounded in continuous bursts for 15 minutes will tell people to make for high ground immediately and avoid using personal transport. A continuous tone for five minutes will sound the all-clear.
Next week's test will familiarise residents with the signals. Each will sound for a minute, starting at noon.
The council says the pole-mounted sirens will gradually increase to full volume, allowing people to "cover their ears while moving away to a safe distance". Each year they will be tested twice, on Sundays at the start and finish of daylight saving.
It is the first tsunami warning system in Auckland, although North Shore Civil Defence manager David Keay said a computerised telephone warning system would be introduced there within three months, capable of alerting more than 14,000 homes in at-risk areas.
Keay said Civil Defence staff around the country had been working on a common warning system since the 2004 Boxing Day tsunami that devastated parts of Asia.
"We were looking for central government to give us a steer, but the years have gone by ... "
Tsunami are most commonly caused by earthquakes under the ocean floor, and can travel thousands of kilometres, reaching speeds of 600km/h.
If New Zealand was threatened, the Pacific Tsunami Warning Centre in Hawaii would alert Civil Defence bosses in Wellington, who would contact local authorities.
But if a tsunami started just off our coastline there would be no time for this process.
"If there is a strong earthquake, people on the ground should take that as their warning," a Ministry of Civil Defence spokesman said.
