Unlike Zara, which operates its website entirely on its own, Uniqlo chose to outsource part of that operation to third-party vendors.

Upon payment, for example, users are redirected to a page tailor-made by Alibaba Group's most popular online marketplace, where transactions and deliveries are fulfilled through the Taobao channel.

Meanwhile, Gap has a hybrid model, with a self-run website on the platform of Tmall.com, the business-to-consumer branch of Alibaba.

A rapid pickup in overseas online purchases has been steered by a policy change allowing third-party payment platforms to offer cross-border consignments.

The green light given by the China State Administration of Foreign Exchange last year enabled people to handle foreign sales and make business purchases.

Chinese consumers can buy products on international websites using domestic third-party payment platforms. There is no need for them to worry about dual-currency credit card issues.

Improvements in logistics also have played a major role.

Shipping products directly from an online shop's main warehouse can be costly for both buyer and the seller. But intermediary logistics firms have come to the rescue.

Foreign fashion brands have to integrate fast search functions, offer popular promotions and, most important, launch China-specific products that are unique to the sites, said Burghardt Groeber, vice-president of Hybris AG's Asia-Pacific branch in Hong Kong, a provider of multichannel commerce software.

"What we are seeing is a growing tension between an authorized site on Tmall and the company's original site. If merchants sell certain items only through the original channel, there will be less dependency on Tmall in the long run," he said.