A major shake-up is looming in the retail sector as the giant online retailer Amazon has its sights set on the Australian market with JB Hi-Fi and Harvey Norman the ones with the most to fear.

Amazon, called one of the largest "disruptors" for retailers, could generate sales of up to $4 billion in Australia with a focus on electrical items, which would be a direct hit on JB Hi-FI and Gerry Harvey's Harvey Norman business.

Brokers have estimated the most impacted retailer is likely to be JB Hi-Fi whose earnings could fall by as much as 23 per cent, followed by a 19 per cent fall in Harvey Norman's earnings.

JB Hi-Fi's sales could fall as much as 6 per cent if Amazon enters this market. There could be about a 2 per cent impact on sales for Myer and Premier Investments because they sell their own merchandise and more Australian-centric brands, retail analysts at stockbroking firm Citi have said.