Five million New Zealanders received last night's emergency alert – here's why you might not have

Around 90 percent of the country received an alert. Photo / File

Phones all over the country lit up and blared a warning last night as Civil Defence tested out its national alerts – but for some, their screens remained silent.

Around 10 per cent of people did not get an alert – and National Emergency Management Agency (NEMA) communications manager Anthony Frith says there are a couple of reasons why that may have happened.

"People may not have been in cellphone coverage, their phones could have been in flight mode or turned off – there could be a variety of reasons to do with the device. It could be an older phone, or the phone could need an update."

Firth says there will be a survey over the next few weeks which will hopefully give NEMA some insight into who is getting the alerts, and how to improve them further.

There's already been a significant improvement since the system was launched in 2017. When it was first used, just one third of New Zealand received the alert.

Firth says some people may have received the alert, but not the loud sound which accompanied it – which is why it's important people fill out the survey on the civil defence site to try to improve things.

He says any feedback is valuable, even if it's just people saying they want to opt out – however, opting out is not an option.

"Emergency alerts are for keeping people safe. You can't opt out, but the bar is very high – it has to be a severe threat for us or any other agency to use it," he told the Herald.

Some examples of a severe threat would be a tsunami, a chemical spill, a fire or flooding.

The alerts were used a lot during the Westport floods, and the 2019 Pidgeon Valley fires.

Even though you can't opt out of the real deal, Firth says there's a work around if you don't want to get the test.

"We advertise it in advance – so people can pop their phone in the other room or turn it off if they don't want to see the test."

Firth says the tests are important as they allow NEMA to check how the alerts would work in a real emergency – but he knows they aren't exactly restful for those who receive them.

"I'd like to thank Kiwis for bearing with us, I know it's not the most pleasant noise but it is really important we test and this gives us confidence it's working as it should."