Hong Kong-based clothing retailer Giordano International issued a profit warning Thursday following weaker sales in mainland China, Bloomberg reported. The company said in a statement to the Hong Kong Stock Exchange that first-quarter gross margins fell to 44.8% from 49.5% a year ago. This, together with a 12.8% fall in overall sales from continuing operations, will have a “substantial negative impact on profits,” the company said. Retail sales in China grew 15% in the first quarter compared to 21.6% for the same period a year ago. Wal-Mart reported that sales in China “were negative in low single digits,” while Convenience Retail Asia, which runs Circle K convenience stores in Hong Kong and the mainland, said first-quarter sales in southern China dropped 6.9%.