LONDON--Luxury clothing company Burberry Group PLC on Wednesday reported a rise in second-half sales, helped by online growth, but said it expects currency movements to hurt profit.

Revenue for the six months ended March 31 rose 19% from the same period last year to GBP1.3 billion ($2.2 billion), the company said, adding that footfall in stores remained soft but online traffic grew.

However, Burberry cautioned that current exchange rates would have a "material adverse impact" on 2015 profit. As an indication, the company said rebasing full-year 2014 retail and wholesale profit for current exchange rates would reduce earnings by about GBP30 million.

"While current exchange rates are a material headwind in what remains an uncertain macro environment, our continued global brand momentum provides an excellent foundation for the future," said Chief Executive Officer Angela Ahrendts. Ms. Ahrendts is set to leave Burberry soon to become retail chief at Apple Inc. and will be replaced by Christopher Bailey, now chief creative officer.

The warning on currencies follows similar comments from the company in January that it would be affected by the strengthening of the British pound because it costs more to translate dollars and euros back into sterling.

Write to Rory Gallivan at rory.gallivan@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires