US discount retailer Costco has funnelled another $110 million to its Australian operations to help fund its rollout of big-box warehouse stores as the world's eighth-largest retailer intensifies the competitive battle with Woolworths and Coles.

The extra dollop of funding from its US parent has already helped Costco construct and open its fourth and fifth warehouse stores in Australia this year, giving it two locations in Melbourne and Sydney. The discounter is already building its sixth store, in Brisbane, and another is to follow in Adelaide soon.

It is believed that Costco is also scouting possible locations for its third store in Melbourne. It opened its maiden Australian Costco warehouse in Docklands in 2009 and a store in Ringwood last month.

Australia has delivered strong returns for the US-based Costco, with fresh documents lodged with the Australian Securities and Investments Commission showing Costco Wholesale Australia raked in $612 million in revenue from shoppers in 2012-13.