The "unique and penetrating sound" was intended to alert mobile phone users to the first national test of the new emergency civil defence alert system.
It was originally due to happen in April 2018 under a contract with the technology's developers in the Netherlands.
The alert test has been brought forward by six months after the public was confused by conflicting information on the risk of a tsunami around New Zealand after the Kaikoura earthquake last November.
Civil Defence and Emergency Management Ministry spokesman Anthony Frith said the Government had spent $18 million on the new mobile-based alert system, including an $800,000 publicity campaign to raise awareness of the first official test between 6pm and 7pm tonight.
Only a third of New Zealand's 5.8 million mobile phones are believed to be capable of receiving the alert - substantially fewer than originally planned.
But that number is expected to grow quickly as new mobile phones are sold and existing phones are upgraded.
The alert will direct people to a text message which in this case will simply explain that it is a test, but which in a real emergency will warn people to leave for higher ground because of a tsunami, or to evacuate an area because of fire risk or a police emergency.
Frith said the sound was easy to deactivate, but warned people not to try to turn it off while driving.
"We advise people to exercise some common sense and pull over if you're driving," he said.
He said the technology had already been implemented in the Netherlands and in other earthquake-prone countries including Chile, Japan, the Philippines and the United States.
Many Vodafone subscribers in New Zealand received the alert by mistake on October 4 when the developers in the Netherlands sent a message out "in error" between 1am and 2am NZ time.
In contrast, today's test is planned between 6pm and 7pm to coincide with the main television news shows to maximise public awareness and minimise panic.
The alerts use a separate channel from normal text messages and will come through on most late-model phones, provided that their software has been updated recently.
People can check whether their phone is set up for the alerts.
On an iPhone, open Settings, select Notifications, and at the bottom you should see a toggle for "Emergency Alerts".
On Android phones the settings vary between different phones but can be found under either Settings or Messages.
Although the phones indicate that the alerts can be turned off, Frith said the New Zealand system had actually been set up so that people could not opt out of it.
"If you really don't want to be disrupted by a rather penetrating noise, we advise people to use flight mode or turn their phones off," he said.
"We encourage them to have their phones on if they can because it will be good to know what the noise sounds like."
