The number of confirmed cases of COVID-19 has risen by 40, officials announced on Tuesday.
Director-General of Health Dr Ashley Bloomfield made the announcement at 1pm.
New Zealand now has 155 cases, including 13 probable cases which would be counted as confirmed, he said.
"In these [probable] cases, this is a person who has returned a negative laboratory test but the clinician looking after the person has diagnosed them as a probable case due to their exposure history and their clinical symptoms," Dr Bloomfield told media.
"These cases are actually treated as if they were a positive laboratory-confirmed case and the actions taken are the same for confirmed cases."
Twelve cases have recovered, while six people are currently in hospital in a stable condition.
A total of four cases are classified as community transmission, three in Auckland and one in Wairarapa. Contact tracing is underway for these.
Dr Bloomfield said around a third of the new cases could be linked to overseas travel or to close contacts of an already confirmed case.
More than 900 lab tests were carried out yesterday and more than 8300 tests have been completed now.
Dr Bloomfield said it was important New Zealand move to alert level 4 as soon as possible.
"There is a clear consensus among public health professionals, scientists and a wide range of health professionals that it is better to do this soon rather than later, and doing so gives New Zealand the best chance of breaking the chain of community transmission," he said.
"This will require all our efforts and I strongly urge all New Zealanders to play their part."
New Zealand going into lockdown
From Wednesday night, New Zealand will be in lockdown for at least four weeks in an attempt to minimise the spread of the virus, which has infected over 150 people in New Zealand.
The lockdown means people must remain indoors, non-essential businesses will close, schools are shut, and travel is severely limited.
"If everyone reduces down their contacts, stays at home, that's one less person that's at risk of picking it up who's less likely to pass it on to three other people and then three other people and then three other people - which is roughly the transmission rate," Prime Minister Jacinda Ardern told The AM Show on Tuesday.
"So everyone needs to play their part, and please do. It's not just about your life, it's about others'."
What we know about coronavirus:
Coronavirus is primarily spread through droplets in the air after someone sneezes or coughs. However, it can also be contracted by touching surfaces where the illness is present, according to the World Health Organization. The length of time the virus stays alive on surfaces is unknown at this stage, but some viruses can remain active for days.
The WHO was first informed of cases of the virus in Wuhan on December 31. It was identified as a coronavirus on January 7 and can spread through human-to-human transmission.
"Common signs of infection include respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. In more severe cases, infection can cause pneumonia, severe acute respiratory syndrome, kidney failure and even death," the WHO says.
"Standard recommendations to prevent infection spread include regular hand washing, covering mouth and nose when coughing and sneezing, thoroughly cooking meat and eggs. Avoid close contact with anyone showing symptoms of respiratory illness such as coughing and sneezing."
There is currently no vaccine for the sickness.
How can I protect myself?
- avoid touching the mouth, nose and eyes with unwashed hands
- washing your hands before eating
- carrying a hand sanitiser at all times
- being particularly mindful of touching your face after using public transport or going to the airport
- carry tissues at all times to cover the mouth and nose when coughing or sneezing (then dispose of it)
- not eating shared or communal food
- avoiding shaking hands, kissing cheeks
- regularly cleaning and sanitise commonly used surfaces and items, such as phones and keys
- avoiding close contact with people suffering from or showing symptoms of acute respiratory infection
- seeking medical attention if you feel unwell.
A full explainer on protecting yourself from coronavirus can be found here.