Countdown supermarkets have placed temporary limits on all products, excluding produce and serviced deli, due to unprecedented demand following the coronavirus outbreak.
It comes as its competitor goes on a hiring spree to cope with demand.
From today, there is a limit of two similar items per customer visit across all Countdown stores and online shopping services.
Baby food (pouches, tins and jars) will have a limit of six.
Countdown said in a statement, the new rule meant customers will only be able to buy a maximum of two packs of toilet paper, two packs of mince, two packets of chicken, two loaves of bread, two cans of baked beans etc.
It has also reduced store trading hours nationwide. All Countdown stores will close tonight at 9pm and from tomorrow, all stores and online shopping services will trade from 9am to 8pm across the country.
Countdown managing director Natalie Davis said the message to New Zealand remained the same: "We are not running out of food".
"We have plenty of food in our supply chain, however we simply cannot get it through the network fast enough if Kiwis don't slow down their shopping. This is the only way we can try to manage demand.
"While this may be frustrating or inconvenient for some customers, we need to provide our team with the time and ability they need to get as much product on shelf as possible during this time of extraordinary demand. If the store is too busy, we will be managing the number of people who can be in our stores at any one time for the safety and wellbeing of our team and other customers."
David asked all New Zealanders to respect the limits and only buy what they needed to help as many Kiwis as possible access food and other groceries.
"We have every truck on the road possible, and every team member possible working to support our stores and online services, and we're hiring more. Every truck that has to go out full of toilet paper means that regular supermarket supplies can't get through.
"We're also working on ways to ensure that customers who need a bit more assistance can get the help they need in our stores and online.
"We would ask all our customers to continue to be kind, consider others and consider what you've got in your pantry already.
"Our teams continue to work tirelessly under difficult circumstances, so we ask that they are treated kindly and respectfully. We thank our customers for their continued patience and support as together we work through these challenging times together."
Meanwhile, Countdown's competitor Foodstuffs - which includes New World and Pak'n Save - is looking for more than 400 staff - over 300 of those are for its stores - as it grapples with a surge in demand.
Supermarkets around Auckland have notices up in their windows seeking urgent help within their stores, some supermarkets have resorted to opening one hour later than usual in the mornings to allow enough time for staff to restock shelves.
Earlier today, Steve Anderson, South Island CEO for Foodstuffs told shoppers to "take a deep breath" and "shop normally".
He said supermarkets were under "huge pressure" and staff were incredibly tired from dealing with the surge of shoppers.
Demand was "just above" levels seen at Christmas time, he said.
"We can handle these sorts of volumes. But we plan for a long time for Christmas. The issue here is that it's arrived and it's unplanned."
He said there was no problem with the supply of groceries because most everyday produce was locally-made.
"While we are currently experiencing a run on demand, it is not a supply issue. Our supply chain is very robust," he said.
"We are fortunate that many of our everyday grocery essentials are made or manufactured right here in New Zealand."
He added: "Shop normally. Our teams have everything in hand and if we all purchase as usual there will be no issues."
Competing supermarkets took the unusual step today of jointly issuing a statement asking New Zealanders to keep calm in the face of Covid-19. Pak'nSave, New World, Four Square, Raeward Fresh, Countdown, Fresh Choice and Super Value made the plea in full-page advertisements.
That came after people responded to the first confirmed cases of coronavirus by panic-buying, leading to long queues at supermarkets and shelves emptied of products like bread, long-life milk and tinned foods.
Supermarkets have come under further pressure as people stock up in preparation for self-isolating at home.
Anderson said there were no plans to introduce "one-in, one-out" rules at supermarkets. And after discussions with Grey Power, they decided it was not necessary for stores to have "elderly hour" sessions.
But there were likely to be limits on some products because of unexpected demand. Anderson encouraged people to seek out alternatives and "be creative" with their shopping.
His main concern was the tiredness of his staff: "I'm really proud of what they've done, but they're getting really tired."
He asked shoppers to be kind to staff and fellow shoppers during the Covid-19 situation.
"These are unprecedented times and shopping normally takes the pressure off our staff who are working hard to ensure that customers get what they need.
"We may all need to take a deep breath or two collectively."
Director-General of Health Ashley Bloomfield said people might want to check their supplies in case of self-isolation, but they did not need to go "above and beyond".
"And also think about the supplies of others who may not be able to get out and ensure they are well catered-for and well looked after."
Bloomfield confirmed today that the number of positive tests for Covid-19 was now 39, up 11 from yesterday.