BEIJING — China’s hottest new online bazaar has had a whirlwind year. The number of people shopping on the app, Pinduoduo, has grown more than fivefold since the beginning of 2017, and its parent company is preparing to list shares on the Nasdaq, one of a wave of Chinese tech companies tapping international capital markets this year.

But by taking its business global, Pinduoduo has exposed itself to a new kind of stumbling block: a trademark infringement lawsuit in the United States.

The complaint, filed Thursday in a federal court in New York by a diaper maker called Daddy’s Choice, says that Pinduoduo knowingly allowed the sale of knockoff products bearing the Daddy’s Choice name. According to the suit, the e-commerce platform removed some of the unauthorized goods when Daddy’s Choice, which is based in Beijing, first reported them last year. But the items quickly reappeared, and Pinduoduo took no action when notified of them again this year, the complaint says.

Lawyers for Daddy’s Choice say in the complaint that they filed the suit in New York because American consumers are able to buy from Pinduoduo, and because Daddy’s Choice has spent considerably to build its brand in the United States. Pinduoduo declined to comment.