Fashion retailer H&M said on Friday sales had fallen during the last three months as fewer shoppers visited its stores, sending its shares plummeting and underlining its struggle to adapt to a shift of business online.

Shares in the world's second largest fashion retailer fell 13 percent to their lowest level since 2009.

H&M CEO Karl-Johan Persson said in a statement that the company's "online sales and sales of the group's other brands continued to develop well" but that physical stores "were negatively affected by a continued challenging market situation with reduced footfall to stores due to the ongoing shift in the industry".

The Swedish group said sales in the September-November period were far below its own expectations. It plans to speed up efforts to adjust to changes in the market, including closing more H&M stores and opening fewer new ones, and start selling the brand through Chinese online platform Tmall.

Sales between September and November dropped by four percent compared to the same period last year to $5.9 million (5 million euros). In local currencies, sales fell by two percent.

"In order to respond even quicker to customers' fast-changing behavior the company's ongoing transformation journey is being accelerated," Persson said.

"This includes continued integration of the physical and digital stores, and intensifying the optimization of the H&M brand's store portfolio -- leading to more store closures and fewer openings," he added.

The group did not specify exactly how many stores would be closed and where.

H&M had announced earlier this year that it would open physical stores around the world to compensate for the downturn due to fierce competition from online sales platforms.

H&M group, which owns other popular brands such as COS, Monki and Weekday, has 4,553 physical stores around the world as of August 31.