While Prime Minister Jacinda Ardern was warning the country not to panic buy on Monday, that was exactly what people started to do.

Before she even finished talking from the Beehive theatrette, the previously-quiet Willis St in Wellington's CBD was packed.

Stuff The line at Pak'n Save in Queenstown.

On Monday afternoon, Ardern announced New Zealand's coronavirus alert level would raise to three, then the maximum of four within 48 hours. All non-essential businesses - restaurants and bars - were set to close, but essential services, such as supermarkets and pharmacies, would remain open.

People were specifically warned against swarming supermarkets, but many ignored that message.

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Kiri Hannifin,​ Countdown's corporate affairs general manager, told RNZ's Afternoons with Jesse Mulligan that stores across the country sold enough food to feed 10 million Kiwis last week. She pleaded with New Zealanders to be kind and not purchase more than was necessary.

"I am asking New Zealand to please not go to the supermarket, we will be open right through this ... we will be open every single day to look after you. There is plenty of food in our country.

"Shop normally, do not stockpile ... because it will break our supply chain."

She said the demand has been hammering Countdown stores and shelves have been "wiped out", which had resulted in a bottleneck in the supply chain.

RNZ Comments on the latest covid-19 measures from Kiri Hannifin of Countdown Supermarkets.

"If you shop us out, then the rest of New Zealand won't have stuff for tomorrow and the next day ... Be decent."

Foodstuffs, which owned New World, Pak'n Save, Four Square, Gilmour's and Trent's, said individual stores were considering reducing operating hours, and staff were beginning to wear protective equipment such as masks.

Contactless online shopping and delivery was available for customers self-isolating or who were unwell. Customers shopping instore were asked to use contactless payment methods, as opposed to cash.

Here's what some Stuff reporters witnessed at supermarkets around the country on Monday afternoon.

WELLINGTON

In Wellington, many shops were closed but the supermarket and pharmacy on Willis St had long queues. Outside New World those queueing were not the recommended two metres apart, and the queue reached down the street with staff controlling entry.

A nearby Unichem pharmacy was temporarily shut down with queues waiting for the doors to open again.

ROBERT KITCHIN/STUFF Immediately following the Prime Minister making the lockdown decision on TV, panic buyer rush to the supermarkets to get supplies.

In the suburb of Island Bay a queue of 30 people formed just to get into the small New World supermarket. A hundred people were already inside, speedily stripping the shelves of everyday essentials - bread, coffee and tinned tomatoes.

John Faa'afu had just come from the gym. He didn't know anything about any lockdown, he just needed to top up on noodles and cereal. He's a traffic controller and had no idea how the restrictions would affect him.

Around 30 people were spotted waiting outside the front doors of New World in Island Bay.

The masked doorman urged people to buy what they needed now, as at level 4 they would only let in 10 people at a time. Inside, the mood was quiet but not panicked. Shoppers waited patiently in line. One older woman just wanted milk. Others had trolleys filled to overflowing.

Chris Rowan came for fresh fruit and vegetables. She had enough basics at home to get by for a while. An educational consultant, she had just come from a school, where the principal and staff were very upset at the announcement of school closures. "It felt like it was war time. That sense of sitting around listening to a radio - or someone's phone."

ROBERT KITCHIN/STUFF Bread and potatoes were essentials for some Wellington shoppers.

She would have no work during the shut-down. As a consultant, showing her wage had decreased from the same time last year would be tricky. However, she was philosophical about the lock-down and thought it was the right decision.

"It is what it is. They made the decision when they said they would. I think Jacinda Ardern has been amazing. I'm feeling bloody lucky to be living in New Zealand."

Across the road at the chemist, an orderly line filed down the footpath, as staff let only one person in at a time. Most were picking up regular prescriptions.

NIKKI MACDONALD/STUFF Shelves at New World Island bay were almost empty.

At the barber, a lone man had his hair trimmed. Kids scooted past on their way home from school, seemingly unaware that their world just shrank beyond recognition.

These scenes were mirrored around the country.

Nikki MacDonald/Stuff Bread was one of the first everyday staples to go.

HASTINGS

There was a forever increasing queue outside Hastings New World as people lined up to get their groceries.

The supermarket's visitor frequency went from fairly normal in the morning to frantic by 3pm. Toilet paper and Steinlager beer were featured in many trolleys, while one woman had six bottles of milk and eight loaves of bread. A woman in the queue was getting noticeably angry at the amount of toilet paper bursting from people's trolleys.

Nikki MacDonald/Stuff The milk supply was also running low.

People in the queue had to wait up to 20 minutes to enter the store. There was little talking among those in the line, as a New World staff member returned every five minutes with abandoned trolleys from the car park.

"It's mad in here," he called to a man who had just parked his car.

AUCKLAND

Abigail Dougherty/Stuff Lines of people form outisde Countdown on Stoddard Road, Mt Roskill.

In Pukekohe, south of Auckland crowds of people had gathered at New World and Countdown supermarkets. One shopper said all of the milk, pasta, bread and flour had been cleared off the shelves.

DARREN BEVAN/STUFF There was controlled entry at Albany Pak' n Save in Auckland.

ABIGAIL DOUGHERTY/STUFF The scenes outside New World on Stoddard Road, Mt Roskill.

"I managed to get a box of dried pasta - but the man behind me in line had two loaves of bread and got into a bit of a verbal fight with a worker about how he could only have one."

Albany Pak'n Save was currently under "controlled entry", only letting a number of shoppers in at a time. Lines of shoppers could be seen spilling into the carpark, many wearing masks, and police were even on hand in store.

Darren Bevan/Stuff Lines of shoppers could be seen spilling into the carpark, many wearing masks, and police were even on hand in store.

Countdown on Richmond Rd in Grey Lynn was so busy shoppers couldn't get in the doors. Security guards could be seen at the entrance.

WARWICK SMITH/STUFF Countdown in Manawatu had its toilet paper shelves almost emptied.

RICKY WILSON/STUFF Pak n Save in Henderson, west Auckland was much busier than usual at 2pm.

CHRISTCHURCH

Christchurch supermarkets were also packed, with some customers taking their own creative measures to prevent the virus spreading.

About 3pm at New World Stanmore in the suburb of Richmond, customers rushed round the supermarket - some with face masks on. One woman even had a tea towel wrapped around her face.

STUFF Toilet paper for sale on pellets at the front of New World Durham St in central Christchurch.

The checkout line was 40 trolleys long, tracking right to the back of the supermarket by the dairy section.

At Durham St New World in the central city, queues were at least ten trolleys long and toilet paper was for sale on pallets at the entrance.

As a result, some supermarkets enforced limitations on various products including paracetamol, chicken, toilet paper, and pasta. New World Albany even closed its doors for a period of time last week because there were too many shoppers.

HANNAH MARTIN/STUFF The queue for the self-checkout aisle at Countdown in Auckland's Ponsonby.

QUEENSTOWN

Police were on the scene at Pak'n Save in Queenstown. They were only let in small groups of shoppers at a time.

Supplied The line was out the door at Pak'n Save's Royal Oak store in Auckland.

In the early afternoon, the queue was quite long.

INVERCARGILL

Inside Pak N Save Invercargill, queues of nine or 10 trolleys waited for each check out and about 40 people wait to go through self service on Monday afternoon.

Police were monitoring shoppers.

WARWICK SMITH/STUFF A lot of people in Manawatu will be living on pasta for the foreseeable future.

A few people were holding their hoods over their mouths or wearing masks.

Across the road at Countdown, the car park was similarly full, as people park wherever they could safely leave their cars.

Queues of about 45 people ran from the check outs.

Shelves were visibly empty or sparse on sugar, risotto rice, vinegar, dish washing liquid and disenfectant.

DARREN BEVAN/STUFF Shoppers queued at Pak'n Save's Albany store with trolleys full of items.

HAMILTON

Hordes of shoppers descended on Hamilton supermarkets, but the mood at each of the businesses visited by Stuff was one of prudence, rather than any kind of mania or panic.

Now apparently well versed in the art of dealing with shoppers descending on the stores en masse, staff were directing the trolley-pushing punters into the interior in an orderly manner.

At Pak'N Save in Mill St, the scene was one not unlike a group of farmers directing their animals into the shearing shed: They were lined up in a semi-orderly manner and ushered through in small numbers, as a similar amount of shoppers, their trolleys fully laden, made their way out the exit.

MARK TAYLOR / STUFF NZ

One couple, who identified themselves only as K Davies and M Hohua, said they had experienced little difficulty getting their shopping, which was their regular weekly excursion. They had expected it would be busy, and had discussed this soon after the Prime Minister's announcement on Monday in an online family group chat.

The mood inside the store was good, Davies said. "Everyone is really friendly. No one has been unreasonable ... This is the best grocery store in Hamilton."

Owner-operator Hamish Walton said: "We are under control."

The carpark at the Nawton shopping centre was half empty at 3:15. At 3:28, it was full.

Long queues were beginning to snake back from every checkout into the aisles at the Countdown supermarket.

A woman who wished to be named only as Wendy said she didn't want to be seen as a panic buyer but was running out of some baking essentials.

"I've only got a tiny amount of flour, a little sugar. I know they say supermarkets will remain open and don't buy in a rush as there'll be plenty of food available, but then each time you look at the shelves there's not much there."

CAMBRIDGE

Supermarket managers in Cambridge, in the Waikato, were working hard to keep the calm as customers flooded their stores.

At Freshchoice in Leamington, owner Richard Jacobsen took on a role more suited for an MC rather than a store manager. Jacobsen, walking around the store with the intercom microphone, reminded shoppers there would be plenty of food for everyone.

He asked people to be calm, to be sensible and to think of others coming in for their groceries too. He also mixed in a bit of humour, thanking customers who had come over from rival supermarkets across town, to do their shopping at Freshchoice.

By 3.13pm, the queue at the tills stretched back to the end of the store and Jacobsen had to ask people to wait at the doors, until enough shoppers left the store to make room for more. About 20 shoppers crowded outside waiting to enter. Jacobsen took the opportunity to remind people about the Ministry of Health precautions, about distancing between people, and correct washing of hands.

On the other side of town, New World also had customers queuing outside while the bigger Countdown supermarket had staff at the entrance to help manage the extra shoppers through the store. Cambridge's pharmacies also had people lining up outside, being tended to by staff wearing masks, offering advice and help.

People finished work a few hours earlier than normal and heavy traffic was noticeable down Cambridge's main Victoria Street. Shops closed early, including the town's many restaurants and cafes, with staff packing away seats and chairs, signalling an end to their trade for the months ahead.

LAWRENCE GULLERY/STUFF Freshchoice supermarket in Leamington, Cambridge.

DARREN BEVAN/STUFF Signs encouraging shoppers to "only buy what you need" were erected at Countdown Ponsonby on Wednesday.

WARWICK SMITH/STUFF There's also a hand sanitiser shortage in Manawatu.

Kai Schwoerer A shopper in Christchurch stocked up on toilet paper, pasta, long life milk and juice.

Hamish Bohny Lines at supermarkets in Christchurch went from one end of the supermarket to the other as shoppers stocked up after the increase in Covid-19 threat level to three.

ANUJA NADKARNI Powdered milk has been a hot commodity for shoppers at Countdown's Lynfield store in Auckland.

ANUJA NADKARNI/STUFF The empty shelves in Countdown's Lynfield store where paper towels and cleaning products used to be.