Customers who order their groceries online are being told they could have to wait up to a week before they can get their deliveries.

Fears about the coronavirus have seen shoppers clearing out shelves in supermarkets in a bid to stockpile items.

Bare shelves have seen many people turn to ordering their groceries online at Coles and Woolworths, but the supermarkets are struggling to keep up with the influx of orders.

Both retailers have been forced to restrict the amount of toilet paper people can buy after it proved to be the item people were most desperate to stock up on.

Shelves have also been stripped of other items such as hand sanitiser, milk, rice, pasta and pasta sauce.

Both retailers usually offer same day delivery, if the order is placed early enough, or next day delivery.

It is typically only orders for "remote" locations that can take up to four days.

But now shoppers are being told it could be up to a week before the next available window for their order.

When news.com.au attempted to place an order with Coles to be delivered to an address in Sydney we were informed it earliest it could arrived would be next Thursday.

Melbourne was slightly quicker, with Wednesday being the estimated arrival time.

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However, the delay appears to be affecting some areas more than others, with Coles saying it could deliver to an address in Brisbane by Saturday.

A Coles spokeswoman told news.com.au that demand for its online services had increased dramatically over the last two weeks.

"We have opened additional delivery windows and have extra delivery vans on the roads to meet the customer demand," the spokeswoman said.

"We apologise to customers if the delivery slot they want is unavailable."

When trying to place an order with Woolworths, Sydney once again had the longest delivery times, with orders not expected until Tuesday or Wednesday.

People in Melbourne would have to wait until Monday, with those in Brisbane told they could get their delivery on Sunday.

A Woolworths spokeswoman said their staff have been working hard to meet the increased demand for deliveries.

"Delivery windows have been filling up faster than usual and we apologise to customers for the inconvenience this has caused," the spokeswoman said.

"We've been ramping up our delivery capacity with the support of our transport partners and doing all we can to fulfil orders for our customers as quickly as possible.

"We thank customers for their patience as we work through this."

Authorities have warned people to stay calm as an increasing number of Aussies rush to the shops to stock up on loo paper.

NSW Premier Gladys Berejiklian on Wednesday said there were no issues with toilet paper supply in NSW and urged the public to refrain from bulk-buying.

"People should just go about their daily business in terms of the products they purchase and I don't see a need to do that (bulk buy) at this stage," she said.

But the message of staying calm and not resorting to panic buying clearly hasn't gotten through to many Australians.