Alipay, a third-party mobile and online payment platform by Alibaba Group Holdings Ltd., is chasing Chinese tourists to Japan, where it's signing up a growing number of retailers and eyeing the long-term potential of the nation's $45 billion digital payments market.

The volume of domestic payments processed on Alipay expanded eightfold in the 12 months to September, said Genki Oka, CEO of the Japan unit of Ant Financial Services Group, which operates the platform. Its network of vendors has climbed to about 38,000 as of November from 20,000 in February, closing in on a target of doubling within a year, Oka said in an interview.

An affiliate of billionaire Jack Ma's Alibaba, Ant Financial entered Japan in 2015 to cater to Chinese visitors who are increasingly shopping with their mobile phones instead of cash. That has stirred worries among the nation's banks that Alipay may eventually offer its services to local consumers as well, challenging their own efforts to develop domestic payment platforms.