Uniqlo, a Japanese apparel chain retailer, this week launched e-commerce in the United States. The launch of a web site where consumers can purchase the retailer’s trendy apparel follows the openings of four Uniqlo retail stores in the United States over the course of the last year, and comes ahead of the retailer’s aggressive expansion plans for bricks-and-mortar stores. The retailer says it plans to open 20 to 30 more stores in North America each year through 2020. It aims to generate $10 billion in North American sales by 2020.

Uniqlo is known as a fast-fashion retailer, meaning it seeks to translate the latest fashion runway styles and get them into stores quickly designing and manufacturing all its own goods to get to market as quickly as possible. Spanish fast-fashion apparel retailer Zara launched U.S. e-commerce last year; Swedish competitor H&M also plans to sell online in the U.S., but has delayed the launch of its e-commerce site to next summer. Zara is part of Inditex Group, No. 141 in Internet Retailer’s Top 400 Europe. H&M is No. 67.

“Opening up our e-commerce store, and making our clothing available to the entire United States is an important part of our long-term growth strategy to be the world’s No. 1 retailer,” says Shin Odake, CEO of Uniqlo USA.

Uniqlo is the largest holding of parent company Fast Retailing Co. Ltd., which also owns several other fashion brands, including Helmut Lang and Theory. Fast Retailing generated 928 billion yen, approximately $11.60 billion, in sales during its 2012 fiscal year. Uniqlo accounted for approximately 83%, or $9.66 billion, of Fast Retailing’s global sales during the year. Outside Japan and the United States, Uniqlo has e-commerce sites for consumers in China, Korea, Taiwan and United Kingdom. It has retail stores in Japan, the United Kingdom, France, Russia, China, South Korea, Hong Kong, Taiwan, Singapore, Malaysia, Thailand and the Philippines. It currently operates five stores in the United States; the latest of which opened in San Francisco less than a month ago.

The U.S. e-commerce site sells apparel for men, women and children, and features more sizes than Uniqlo sells in its retail stores, the company says. For example, women’s leggings are available in sizes ranging from XXS to XXL, whereas in stores they are available only in XS to XL. Free standard shipping is available on orders greater than $100 and Uniqlo says consumers can expect delivery in one to five business days. Standard shipping on orders less than $100 is $7. Overnight delivery is available for $22, although consumers who live in areas of the Northeast near Uniqlo’s fulfillment center in Secaucus, NJ, can get overnight delivery for $7. Online purchases can be returned to Uniqlo stores.

Uniqlo says it used vendors Razorfish and Digitas, both of which provide digital marketing services, to design the U.S. e-commerce site. A spokeswoman says Uniqlo will develop site content and Razorfish will update and run the e-commerce site.

For more about global opportunities for e-retailers, read the upcoming November issue of Internet Retailer magazine.