A new emergency alert system which sends alerts to cellphones around New Zealand is being rolled out across the country.

Led by the Ministry of Civil Defence and Emergency Management (MCDEM), the alerts will be sent out if life, health or property is in serious danger.

A nationwide test of the emergency mobile alert is happening on November 26 - Sunday week - between 6pm and 7pm.

Emergency Mobile Alert messages can be sent only by MCDEM, Civil Defence Emergency Management Groups, police, Fire and Emergency, the Ministry of Health and the Ministry for Primary Industries.

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Whanganui District emergency management officer Anthony Edwards said people don't need to sign up or download an app, as the alerts are sent using cell broadcast technology.

"If your phone is capable of receiving emergency mobile alerts, the alert should appear automatically on your phone's screen with a unique and penetrating warning sound. As it is about keeping you safe, you won't be able to opt out of receiving it," Mr Edwards said.

"It is expected around one third of phones will initially be able to receive the alerts. This number is expected to rise substantially over time as people replace their phones with newer models."

Mr Edwards says because the Whanganui District is at risk from several emergency event scenarios such as floods, extreme weather, earthquakes, tsunami and volcanic eruptions, the emergency mobile alert is another way people can be effectively warned and quickly find out what to do when there is an emergency.

You can check whether your phone will receive the alert and find out more at civildefence.govt.nz.