Guanze Medical Information Industry (HKG:2427) flagged a high concentration of shareholding in the firm's shares following a request from the Hong Kong Stock Exchange, according to a filing with the city's bourse Wednesday.

The medical imaging film products maker's shares fell nearly 17% in late morning trade Thursday.

According to the notice, 20 shareholders collectively controlled 94.13% of the company's issued share capital, leaving only 5.87% of the issued shares in the hands of other shareholders.

This meant that the shares may not have a genuine market and prices could fluctuate "substantially" even with a small number of shares traded, the firm said.