An early morning text from Civil Defence to thousands of Kiwi cellphones has made many grumpy today.

Even more confusing and aggravating was picking up the phone and learning the first message at 1.32am was "just a test" of the emergency alert system.

But it didn't stop there, and people reported receiving several messages until 2am. Civil Defence has since apologised and assured people it won't happen again.

One blurry-eyed Herald reader wrote to the newsroom at 2.05am: "Hi why are Civil Defence testing their txt messaging system between 1.30am and 2.00am?? I jus receive 3 messages', they wrote.

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Another emailed in shortly after.

"Why am I receiving Emergency Mobile Alert test messages between 1.30am and 2am?

"After the third message blared away I've turned emergency alerts off in the hope I might not get woken again. Is this the desired result of your testing?"

Twitter was also flooded with tweets from angry users.

Civil Defence tweeted at 3am - hopefully not waking those who had just got back to sleep - apologising to those who received the alert at an "inconvenient hour".

It tweeted again that it in future it would send the test texts out "during daylight hours from now on".

Director of the Ministry of Civil Defence and Emergency Management Sarah Stuart-Black told Newstalk ZB the test text messages were sent to the public "in error" for which she apologised.

"A set of three text messages were sent to the public in error when they were supposed to be restricted to a contained testing environment and the result has been that many New Zealanders were woken from their sleep at 1.30am and would have received up to three messages.

"It is completely unacceptable and I take full responsibility and certainly apologise to every person that was woken by the messages."

Stuart-Black said the texts were sent by the provider of the technology who is based in Europe. She has vowed the mistake will not happen again.

"There was something in the system that hadn't restricted it to just in that testing environment so it went to the wider public so I have sought assurances that safeguards are put in place so that this doesn't happen again."

She accepted that the noise made by the text alerts was no ordinary text message sound.

"I know it would have been alarming to have been woken like this. It's not a normal text message sound. It's designed to make a noise that really gets your attention and for that reason it would have given people a real fright being woken from a deep sleep by such a noise not understanding what the purpose of this was."

The alerts would have only been on Vodafone mobiles, she said, but stressed that it wasn't the company's fault.

She said the emergency mobile alerts, which are due to be launched before the end of the year, are a "potentially life-saving alerting system" and she hoped it wouldn't discourage the public.

"I would hope not. This is a really amazing piece of technology and we are putting it in place to make sure New Zealanders are safe to make sure that they have information either just before an emergency happens or during emergencies so they can keep themselves and their families safe."

The apology is likely cold comfort to those already reaching for their second coffee of the day.