The state of national emergency was declared by Minister of Civil Defence Peeni Henare under the Civil Defence Emergency Act 2002, Director of Civil Defence Emergency Management Sarah Stuart Black said on Wednesday in a conference.

"The state of national emergency has been declared because of the unprecedented nature of this global pandemic and to ensure the government has the powers it needs to slow the spread of COVID-19 and reduce its impact," she said.

New Zealand confirmed 50 new COVID-19 cases on Wednesday, bringing the total number of the confirmed cases in this country to 205, according to the Ministry of Health.

"Today we put in place our country's second ever State of National Emergency as we fight a global pandemic, save New Zealanders' lives and prevent the very worst that we've seen around the world from happening here," Prime Minister Jacinda Ardern said in a television speech in Parliament after the state of national emergency was declared.

"As the country moves into Alert Level 4 - Eliminate, at midnight, we need all the tools at our disposal to ensure everyone reduces down contact with one another across the board.

"Through the early and hard measures we've taken at the border, using the powers under the Health Act, the signing of Epidemic Notices, and now, being in a State of National Emergency, we have all of the legislative means possible, all the enforcement powers, all the tools we need, at our disposal to combat the spread of COVID-19."

Under the Civil Defence Emergency Management Act 2002, the state of national emergency declaration allows the Director Civil Defence Emergency Management to direct and coordinate personnel, material and other resources, and provides access to other extra-ordinary powers that will support delivery of an effective and timely response to COVID-19.

While in force, the state of national emergency will allow the director and local controllers, as needed, to provide for the conservation and supply of food, fuel and other essential supplies, regulate land, water and air traffic, close roads and public places, evacuate any premises including any public place and if necessary to exclude people or vehicles from any premises or places.

"Failure of anyone to play their part in coming days will put the lives of others at risk, and there will be no tolerance for that," the prime minister said.

"We do not expect to use the full extent of these measures but, as with everything we have done in response to COVID-19, we plan, we prepare, we have in place everything we need to get through."

"For now, I ask that New Zealanders do their part. Stay home, break the chain, save lives," Jacinda Ardern said.