Myer has closed its website "until further notice" at the height of the summer sales season, robbing Australia's biggest department store of online sales.

The website crashed on Christmas Day and was down for most of Boxing Day and all of Friday.

Online shoppers have been left out of Myer's post-Christmas sales rush, with the store's website down until further notice. Credit:Penny Stephens

It means Myer will see no benefit for those days from booming domestic online sales, which were tipped to hit $344 million across the retail sector on Boxing Day alone.

"We're continuing to experience significant issues with our website, and as a result we will not be activating the site for customers until we are confident the issues have been resolved," Myer said in a statement on its Facebook page.