The 150-plus tsunami sirens stringing Northland's coast will be sounded when daylight saving starts later this month - not to herald summer, but to ensure the warning system works.

Coming soon after a tsunami warning following an earthquake off East Cape, the six-monthly test is timely.

The 150-plus Northland sirens will sound on the morning of Sunday, September 25, as part of the regular twice-yearly checks.

Victoria Randall, of the Northland Civil Defence Emergency Management Group, said the sirens will sound twice - at 9.20am for 10 minutes and at 10am for 30 seconds.

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"Civil Defence community groups or local council staff will monitor the sirens at these times, reporting any faults for repair," Ms Randall said.

The siren network comprises 85 in the Whangarei district, 58 in the Far North and 14 in the Kaipara district.

The shoebox-sized units, each with a siren, flashing light and blue and yellow Civil Defence logo, are attached to power poles in communities along the coast.

In the event of a real tsunami warning, the sirens are an indicator to local communities to seek further information.

"Rather than triggering evacuations, tsunami sirens are designed to alert people that they need to seek further information about potential tsunami risks from official sources," Ms Randall said.

It is possible, though, that tsunami could arrive before an official Civil Defence notification.

Natural warnings following an earthquake include unusual sea behaviour such as a sudden sea level fall or rise, and loud or unusual sea noises, particularly roaring like a jet engine.

Coastal households in areas at risk from tsunami should have a plan in place. People should immediately go to higher ground.

Information is available from www.nrc.govt.nz/civildefence or from www.facebook.com/civildefencenorthland.