New Zealand is preparing to enter a month-long nationwide lockdown from Wednesday night, with the entire country ordered to stay home apart from those in essential services.

On Monday the nation was given two days to prepare for schools, businesses and community services to turn off the lights in a desperate bid to stem the spread of the coronavirus. The move came after the number of cases of Covid-19 in New Zealand rose past 100.

In an address to the nation, the prime minister, Jacinda Ardern, said she was not willing to put the lives of her citizens in danger.

“The worst-case scenario is simply intolerable, it would represent the greatest loss of New Zealanders’ lives in our history and I will not take that chance.” Ardern announced the country would move to level three measures immediately, and then to four – the highest level – on Wednesday from 11.59pm.

“I say to all New Zealanders: the government will do all it can to protect you. Now I’m asking you to do everything you can to protect all of us. Kiwis – go home.”

The lockdown will last a month, and if the trend of cases slowed, could be partially eased in specific areas after that. Ardern said it was now established that community transmission was happening in New Zealand and that, if it took off, the number of cases would double every five days, with modelling advising the government that tens of thousands of New Zealanders could die.

“The situation here is moving at pace, and so must we. The trajectory is very clear, act now or risk the virus taking hold as it has elsewhere.”

Possible coronavirus patients are tested in Auckland. Photograph: Greg Bowker/Getty Images

“We currently have 102 cases, but so did Italy once, now the virus has overwhelmed their health system, and hundreds of people are dying every day.”

Ardern said if the country did not lock down it would face a death toll beyond anything ever experienced before, and she wanted to give health services “a fighting chance”.

Thirty-six new cases of the coronavirus were confirmed on Monday, bringing the nationwide total to 102, spread across the North and South islands.

Ardern said she knew the measures would be anxiety-inducing for many New Zealanders and they needed to be “strong and kind” to each other during the unprecedented crisis.

“Today, get your neighbour’s phone number, set up a community group chat, get your gear to work from home, cancel social gatherings of any size or shape, prepare to walk around the block while keeping a two-metre distance between you.

“If in doubt, don’t go out.”

Following the prime minister’s announcement there were immediate reports of panic buying at supermarkets and liquor stores around the country, with lines down the street for both. Panic-buying has not occurred in poorer neighbourhoods, some locals reported, mainly because residents of those suburbs did not have any spare cash for stocking up.

Many phone lines jammed on Monday afternoon as New Zealanders frantically rang and texted each other, making plans for the coming month.

Essential services such as supermarkets, pharmacies and doctor’s clinics, service stations and petrol stations will remain open throughout the lockdown. Ardern urged people to avoid the supermarket if they did not have urgent needs.

The Ministry of Health was also working on an urgent plan to support mental health while they remained indoors through April, Ardern said.

“We are all as a nation preparing to go into self-isolation, in the same way we have seen many other nations do.

“These measures will place the most significant restrictions on New Zealanders’ movements in modern history, this is not a decision taken lightly but it is our best chance to slow the virus and save lives.”

“I know what I am asking for is significant, but I ask New Zealanders to move through this next phase in an orderly way,” Ardern said.

People could still go for a walk, take children out for fresh air and walk their pets, Ardern said, but must stay away from anyone not in lockdown in their own homes.

Enforcement would be provided by police officers and the military, and the government urged New Zealand not to take vigilante policing measures into their own hands – “that’s our job”, she said.

Finance minister Grant Robertson did not rule out that a universal basic income for all New Zealanders may be introduced, or that New Zealanders may be able to access their superannuation accounts early, as those in Australia now can.

Robertson said the entire shutdown of the country has the resounding support of the business community, and was seen as the best chance to help the economy recover down the track.

On social media many were shocked by the prime minister’s announcement, but applauded her calm and leadership .

The opposition leader, Simon Bridges, and many prominent scientists and health experts have been calling for an entire nationwide shutdown since last week, and applauded the government taking the action so quickly – far ahead of many European countries who are now dealing with hundreds of deaths.