The fine was issued by the Beijing office of China's foreign exchange regulator, it said.

Chinabank Payments said in a statement that in 2017 the platform had been negligent with some of its users' access, which was then exploited by a number of external merchants to make illegal transactions.

It said it had expelled those merchants after an internal investigation found problems.

"Chinabank Payments seriously reflected on our business management and carried out rectifications. We apologise for the negative impact we caused to the industry," it said, adding that the firm was supportive of the regulator's decision.

(Reporting by Winni Zhou, Andrew Galbraith and Brenda Goh; editing by Louise Heavens and Jason Neely)