Civil Defence earlier said a nationwide mobile alert would be issued to all New Zealanders between 6-7pm.
Emergency alerts can be sent "if your life, health or property is in danger" without needing to sign up or download an app, Civil Defence says on its website. But phone owners must ensure the operating system software is updated.
Most phones sold by 2degrees, Spark and Vodafone are known to receive the alerts - about four million phones.
If your phone is from overseas or parallel-imported, "your experience may differ from those sold in New Zealand".
They are broadcast from targeted cell towers so they work in areas where there is coverage (about 97 per cent of populated areas). They are targeted to areas affected by serious hazards. Specific phones cannot be excluded and the alerts cannot be responded to.
They may not work if mobile phone towers are damaged or if there is a power outage.
"If you get an alert, read the message and take it seriously. It will tell you what the emergency is and what to do," Civil Defence says.
"It will also tell you which agency sent the message and, if needed, where to go for more information."
Police, Fire and Emergency, the Ministry of Health and the Ministry of Primary Industries can also send alerts.
Unlike text messages, mobile alerts are very secure and don't require the private details of recipients. They do not use your mobile phone number and it is impossible to collect information about you, your cell phone use or your location.
"You still need to be prepared for an emergency and you should not wait to get an alert before you act," Civil Defence says.
"If you feel your life is in danger, don't wait for an official warning. Take immediate action.
"Make sure you have your own emergency plan that includes what to do, where to go, who to go to for help and who you might need to look out for."
State of emergency explained
Civil Defence's State of Emergency was declared at 12.21pm and applies to all of New Zealand - including the Chatham Islands, Stewart Island and other inhabited islands.
Legislation allows it to be in place for seven days and can be extended.
The Minister for Civil Defence Peeni Henare announced the emergency.
The National Emergency Management Agency (NEMA) supports Civil Defence Emergency Management (CDEM) Groups in their planning and operations.
NEMA is in charge in a State of National Emergency. CDEM says these types of emergencies are rare. The only one like this was the Christchurch Earthquake of February 2011.
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Earlier this week, Civil Defence Emergency Management (CDEM) director Sarah Stuart-Black said powers under a national state of emergency would "enable us to be able to close or restrict access to roads or public places, remove or secure dangerous structures or materials, provide rescue, first aid, food, shelter, conserve essential supplies, regulate traffic, dispose of fatalities in terms of people that have passed away or animals, enter into premises to rescue people or save lives, evacuate premises or places, remove vehicles and vessels, requisition equipment and materials and assistance".
She said tasks required by CDEM would be carried out be central and local government, emergency services, the defence force and a range of other agencies.
Today, Stuart-Black said the State of National Emergency provided access to powers that were not normally available, but were necessary.
She said the powers were complementary to the powers held by the Director-General of Health.
New Zealand police are responsible for the maintenance of law and order during an emergency, the National CDEM Plan 2015 says.
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They may exercise special powers during a state of emergency, and will liaise with other agencies to ensure the most effective use of police resources.
In comment provided by the Science Media Centre, Professor Andrew Geddis from University of Otago, said:
"With the declaration of a state of emergency and issue of an epidemic notice, New Zealand's government has taken on powers that haven't been seen since the 1951 Waterfront dispute.
"The police (and the army, if needed to support the police) are empowered to order any person to stop any activity that contributes to the current emergency - essentially, spreading Covid-19 in the community. Government ministers may set aside virtually any legislative provision that becomes impracticable to apply while the epidemic is in force.
"These give the state extraordinary reach into our lives, and transfer extraordinary power to the executive branch. They are a marker of just how severe the threat that this virus poses to us all."
