Canada's grocery stores won't run out of food and essentials despite unprecedented demand amid the novel coronavirus outbreak, chief executives of the country's big grocers say.

But they add it may take some time to restock certain products in some stores.

"The issue, of course, is that we're seeing demand in our stores of historic proportions -- never before seen," Michael Medline, CEO of Empire Co. Ltd., said in an interview.

Empire owns Sobeys and Safeway in Canada.

Over the company's 113 years in business, it has never experienced such an influx of customers, Medline wrote in an open letter to customers dated Monday.

Canadians have flocked to grocery stores in recent days to stock up on food and supplies as the country recorded more cases of coronavirus, resulting in crowded stores and photos circulating on social media of empty shelves.

"There will be shortages in every grocery store in different categories on a daily basis because demand is outstripping any way you could possibly amp up your supply," Medline said in an interview.

But the company's staff is working with suppliers to replenish any temporarily out-of-stock products and keep shelves full.

In some cases where it's more efficient, the company's suppliers are transporting their products directly to stores rather than Empire's distribution centres.

"The food supply chain in this country is working better than it ever has before because it's a crisis," Medline said.

Canada's largest grocer, Loblaw Companies Ltd., also sent a letter to customers, reassuring its loyalty program members not to worry.

"We are not running out of food or essential supplies," wrote chief executive Galen Weston, adding the company's supply chain and store teams are working on getting the most important items back on store shelves, though some products, such as hand sanitizer, may take longer to restock.

"Volumes are already normalizing somewhat, and we are catching up," he wrote.

The company is also planning for contingencies, said Catherine Thomas, a Loblaw spokeswoman, to ensure it can continue to serve Canadians under a number of possible scenarios.

Metro Inc., which owns and operates about 950 grocery stores and 650 drugstores under a number of banners, posted a letter from its CEO on the company's website saying it is "taking the necessary steps to avoid stock shortages as much as possible."

Stores can limit customers to two products each of high-demand items, Eric La Fleche wrote.

"Our distribution centre, store, pharmacy, and online grocery teams are making every effort possible to ensure product availability and to meet the recent spike in demand," La Fleche said.

Metro spokeswoman Marie-Claude Bacon said a shopping frenzy last Thursday created a rare situation and the company has worked closely with its suppliers and warehouse teams to restock products.

"The situation has been improving over the last few days and is going to continue to improve over the rest of the week," she said.

Stores shouldn't be sold out of any type of product now, but may still be lacking the full assortment, she said, meaning customers should, for example, be able to buy toilet paper, but may not be able to purchase their favoured brand.

"But shortly you'll be able to find the usual brands that you shop in our stores."

Costco sent a letter to members from its CEO on Tuesday saying that the company is enforcing purchase limits on some items.

"Our buyers and suppliers are working to ensure in-demand merchandise as well as everyday favourites are available in our warehouses," said Craig Jelinek.

Sobeys and Loblaw both say they won't hike prices of any products to take advantage of the demand, and are introducing a special shopping hour for seniors and other at-risk folks who need to shop in person to do so without battling the broader crowds.

Those who can should stay home, said Medline, but some will need to shop in person.

The company is asking its customers to respect that the first hour of operation daily at many of its stores is now reserved for seniors and at-risk populations.

Loblaw customers should check with its local stores to confirm whether this so-called seniors' shopping hour will be within existing or adjusted hours, Thomas said.

Metro is also committed to not raising prices amid the outbreak and is looking into a seniors' hour, but is seeking guidance from government and health authorities, Bacon said.

The companies are working hard to keep food on the shelves and offer people a safe shopping experience.

"We never thought ... that grocery stores would be essential services... the front line," said Medline, calling his staff, especially the cashiers "absolute heroes" during the outbreak.

This report by The Canadian Press was first published March 17, 2020.