BEIJING — JD.com Inc., China’s biggest online retailer, and Canadian e-commerce service Shopify announced a strategic cooperation today to give independent U.S. merchants access to JD.com’s 550 million customers.

The companies said the tie-up would allow U.S. brands to start selling in China in three to four weeks compared with up to a year typically required to launch cross-border sales.

The service will take advantage of JD’s network of 1,300 warehouse and 200,000 delivery personnel in China, the companies said. They said it will provide translation and other support.

JD.com reported sales rose 33% over a year earlier to $34.4 billion in its latest quarter.