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A new high-tech warning phone system will soon be available for residents on Auckland's North Shore to alert them of a tsunami, a move council and civil defence officials hope will save lives in an emergency.

The tsunami alert system, designed to warn 15,000 homes and businesses in a matter of seconds, was approved by North Shore City Council and Civil Defence to prepare for a tsunami. It is expected to be operational by July.

Residents living in coastal areas identified as danger zones will receive a letter next week inviting them to join in the city's new high-tech telephone alert system - one of the first of its kind in New Zealand.

Homes up to 15 metres from the coast along North Shore City will be sent the letter, from Long Bay, through the East Coast Bays to Devonport and the upper harbour suburbs. Lake Pupuke is also identified as high-risk.

North Shore Civil Defence manager David Keay was looking forward to the implementation of the alert.

Mr Keay said: "We're one of the first in this country to implement a telephone-based tsunami alert system, an invaluable tool for our unprotected coastline and position on the Earth's 'ring of fire'.

"We see this system as the best fit for our landscape and are confident that all residents in high-risk zones will appreciate the importance of an alert system that could save lives."

Homes and businesses in the most at-risk areas will be invited to opt in to the alert system, either by filling in their contact details online with an individual code, or returning the slip provided on the letter.

North Shore City's Actionline call-centre manager, Ann Hollway, said the technology could handle a large volume of traffic in the event of a tsunami warning.

"We tested the system last year on a small scale and it was highly efficient.

"We will soon be ready to test it on a larger scale and we urge all households requested to opt in by June.

"Because no one knows when a tsunami may strike, our best defence is to be prepared and that involves testing the system with as many participants as possible."

When a tsunami is declared by National Civil Defence, the system is activated to automatically send telephone calls to those listed on the alert database.

The automated voice message will announce a Civil Defence tsunami alert and the listener will be directed to immediately tune into Newstalk ZB Auckland, or Radio New Zealand, for emergency instructions.

The alert message will also advise users to avoid using telephone networks to prevent overloading.

No national warning system has been recommended or operated by the Ministry of Civil Defence.

Details provided to the council when opting in to the system will be used for Civil Defence purposes only.

Some local authorities, including the Rodney District Council, have taken up a text message warning service to alert residents who register their mobile phone number to the risks of natural disasters such as storms or tsunami.