Queueing outside insurance sales offices is not a normal Friday night activity in any part of the world. So when Chinese citizens started lining up to see insurance agents in Hong Kong last month, it was clear that something was amiss.

Mainland Chinese customers have been buying life insurance in Hong Kong for more than a decade. The pace has quickened over the past 15 months, however, with some people paying millions of dollars in premiums as a means of moving their cash offshore and into a different currency.

But China UnionPay, the state-backed bank card monopoly that has acted as the primary conduit for purchases of insurance policies in Hong Kong, has moved to limit use of the channel, delivering what is likely to be a blow to the rapid growth in premiums many insurers have enjoyed over the past year.