Target Corp's (TGT.N) quarterly comparable sales fell more than expected and the retailer slashed its full-year profit forecast as it faces increased competition from online rivals and demand eases for clothes and electronics.

Target's sales, like those of its rivals, have suffered as shoppers increasingly use online retailers such as Amazon.com (AMZN.O) and focus their spending on home renovations and big items such as cars rather than on clothes and electronic gear.

The Minneapolis-based retailer's shares were down 2.6 per cent at US$73.50 in premarket trading on Wednesday.

Up to Tuesday's close, they had risen nearly 4 per cent since the start of the year.

Target's sales at stores open for at least a year fell 1.1 per cent. Analysts on average had expected same-store sales to decline 1 per cent, according to research firm Consensus Metrix.

"Based on the current retail environment the company believes it is prudent to lower its expectations for comparable sales in the second half of the year," the company said.

Target said it expected same-store sales to be flat to down 2 per cent in the second half of the year and cut its full-year adjusted profit forecast to $4.80-$5.20 per share from $5.20-$5.40.

Net income attributable to the company fell nearly 10 per cent to $680 million, or $1.16 per share in the second quarter ended July 30.

Excluding items, Target earned $1.23 per share. Net sales fell 7.2 per cent to $16.17 billion. Analysts on average had expected earnings of $1.12 per share and revenue of $16.18 billion, according to Thomson Reuters I/B/E/S.