Hennes & Mauritz said sales rebounded in September after unseasonably warm weather prompted the world's second-biggest fashion retailer to report its weakest monthly sales growth in over two years for August.

The Swedish budget retailer said sales from September 1 to September 22 rose 12% in local currencies, up from a rise of just 1% in August. 

"When the weather became more normal in September, sales took off again and we are looking forward to an exciting fashion autumn," chief executive Karl-Johan Persson said in a statement. 

Last week, rival Inditex reported a brisk start to the autumn season, with sales in local currencies in the six weeks to September 10 up 16%. 

H&M said pretax profit was largely unchanged at 6.94 billion crowns ($826m) in the months from June to August from a year earlier compared to a mean forecast in a Reuters poll of analysts for 6.93 billion. 

H&M, which has been slower than Inditex to offer its garments online, said it planned to extend e-commerce to another nine markets including Japan and Ireland in the next financial year on top of the 23 markets it will cover this year.

It also reiterated it plans to open about 400 new stores this year, including 240 it expects to open in the fourth quarter - almost three new stores a day.