The National Emergency Management Agency (NEMA) will be testing its Emergency Mobile Alert on Sunday evening.
"There will be a phone alert you can’t ignore – but don’t worry, it’s just a test," NEMA said in a media release on Friday.
"This year’s nationwide test of the Emergency Mobile Alert system will take place on Sunday 22 May between 6-7pm."
It is expected the test will trigger alerts on over 5 million phones across New Zealand, reaching nine in ten people.
Director of Civil Defence emergency management Gary Knowles outlined why the test is taking place.
"The nationwide test is a way to check our systems, the cell towers and your phone’s ability to receive an Emergency Mobile Alert, so we have confidence it will perform as it should in an emergency."
As long as your phone is on you should receive the alert and there is no opting out.