Bourke Street Mall may be the beating heart of Melbourne's vibrant shopping scene, but some retailers are cracking amid tougher than expected trading conditions.

The mall, the city's main pedestrian shopping thoroughfare, has some of the city's most sought-after retail real estate - commanding correspondingly steep rents - and is home to flagship department stores Myer and David Jones.

The lure of shoppers flocking to Bourke Street made it the location of choice for well-resourced international fast fashion brands H&M and Zara when they established their first Australian stores several years ago.

But soaring rents and tougher trading conditions are giving some local retailers second thoughts.