"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.