Mosaic operates brands including Katies, Rockmans, Millers, Noni B, Rivers, Autograph, Crossroads, W.Lane and beme, with up to 500 stores looking set to close.

The retailer announced its end of financial year results on Tuesday with Mosaic chief executive officer Scott Evans telling shareholders the company had been left ravaged.

"The forecast was utterly derailed, first by the devastating bushfires which directly impacted 20 per cent of our store portfolio over the Christmas period, then by COVID-19 which saw us close all 1333 stores for 9.5 weeks including the peak Mother's Day trading period," he said.

"The retail rental market in Australia is not paused because of the pandemic, it is fundamentally changed for the future.

"There is no road map to navigate these circumstances, but our operational priorities have been ensuring team and customer safety, reducing inventory and maintaining a strong cash position."

Mosaic reported a statutory loss before tax of $212.1 million, a huge decline on the prior year's statutory profit of $11 million, partially due to $113.5 million in impairments of the company's brand names and other goodwill. Shares plunged 20 per cent to 54 cents following the result.

Revenue fell 16.5 per cent to $736.7 million.

Underlying earnings before interest, tax, depreciation and amortisation (EBITDA) fell 200 per cent to a loss of $45.8 million, which included a provision of $49 million for unpaid rent.

Online sales grew by just 14.7 per cent year-on-year.

The announcement to shareholders said Mosaic would shut between 300 to 500 stores within the next 12 to 24 months.

Currently around 41 per cent of store leases are on holdover or expiring by this December, with 87 per cent due to expire within two years.

Mosaic has 6000 employees across Australia and Mr Evans said exact locations of store closures and numbers are to be determined.