Nasdaq Inc. is cracking down on initial public offerings (IPOs) of small Chinese companies by tightening restrictions and slowing down their approval, according to regulatory filings, corporate executives and investment bankers.

Nasdaq's attempt to limit these stock market flotations comes as a growing number of them end up raising most of the capital in their IPO from Chinese sources, rather than from U.S. investors.

The shares of most small Chinese companies trade thinly following their U.S. listing, because most of them stay in the hands of a few insiders. Their low liquidity makes them unattractive to many large institutional investors, to whom Nasdaq is seeking to cater.