Apparel giant Gap Inc's woes continued on Thursday when it reported a two per cent slide in September same-store sales and warned fourth quarter earnings could be hit by West Coast port closures.

The San Francisco-based operator of more than 4,200 stores said total sales for the five weeks ended October 5 climbed six per cent to $1.3 billion from $1.2bn in the year-ago period.

By division, Gap's domestic same-store sales fell three per cent while Gap international's same-store sales rose three per cent. It added Old Navy's same-store sales fell two per cent last month as did Banana Republic's.

"Overall, the negative traffic trends and promotional retail environment experienced in August continued throughout September, which led to an increase in promotional activity," said CFO Heidi Kunz.

"However, compared to last year, we sold less at markdown and had better markdown margins, resulting in a year-over-year improvement in total company margins."

Commenting on the impact of the West Coast port closures, Ms Kunz added: "For all three brands, the closures have impacted the receipt of holiday merchandise that was anticipated to be delivered to stores in late October and mid November.

"As a result, we expect portions of the holiday flows to arrive in-stores up to a few weeks later than the original anticipated in-store dates."

Gap said it does not expect the closures to hit third quarter earnings but it sees a fourth quarter earnings risk of between two and seven cents per share, assuming the ports remain open.

The company added its year-to-date sales of $8.6bn for the 35 weeks to October 5 are down one per cent from 2001 while its year-to-date same-store sales are down nine per cent from the year-ago period.