Coles is road-testing a new way for customers to buy and pick up their groceries. Shoppers in Melbourne order online and then collect the items from secure refrigerated storage at a time convenient to them between 3pm and midnight. Now, there are plans to trial the system in Sydney, possibly this year.

The general manager for online at Coles, Keith Louie, said that its internet sales had grown five-fold over the past four years and predicted ''strong double-digit'' growth in online food shopping over the next three years.

The online service has changed dramatically from five years ago, Mr Louie said, when distribution in Sydney and Melbourne was conducted from a single centre in each city with a fleet of 10 vehicles. Now, 48 service stores across Australia reach 92 per cent of the population with delivery from refrigerated van to kitchen benchtop costing consumers about $9.

But some customers want the chance to pick up groceries at their convenience. ''Some customers, particularly busy working customers, have said they would love to have groceries delivered but some don't know if they are going to leave the office at 5, 6, 7 or even 8 o'clock,'' Mr Louie said.

Coles already offers a ''click and collect'' program in nine NSW stores, where customers buy online and go into the store to pick up their purchases.

A research consultant at Monash University, Selma Mehmedovic, said online sales were ''still quite small''. ''In general, online retailing only accounts for 5 to 6 per cent of sales overall … it is growing much faster than traditional retailing,'' she said.

''Customers are becoming more comfortable with shopping online and using mobile phones to scan items they have run out of to process an order. These technologies are making that process much easier for the customer.''

Woolworths also sees potential in the convenience shopper. Its chief executive, Grant O'Brien, last month announced that for the year to June, online sales increased 95 per cent. The figure included online operations of Woolworths, BIG W and Dan Murphy's as well as Cellarmasters, a purely online liquor retailer.

''Even if you strip out Cellarmasters, the growth is still 48 per cent which is still far larger than the growth in the bricks and mortar stores,'' Woolworths said. A Woolworths spokeswoman, Siobhan Quinn, said customers were constantly asking for flexibility around how and when they shop.

This month, Woolworths launched a ''click&collect drive-thru supermarket'' at Warringah Mall, which it says means ''no delivery charges, no waiting and no need to get out of your car''.

Customers use a mobile phone app to make purchases.

Woolworths also recently conducted a trial at Town Hall station where commuters could use scanning technology to buy products.