Chinese authorities have stepped up their crackdown on short-selling of shares, with the two main stock exchanges unveiling new rules that would make it even more difficult for speculators to profit from hourly gyrations in stock prices.

The Shanghai and Shenzhen exchanges said in separate statements on Monday night that the rules, effective immediately, would prevent traders from borrowing and repaying stocks within a day.

China's exchanges and markets watchdogs are cracking down on short-selling as part of a broad government-orchestrated effort to prevent a collapse in its markets, which have already lost about 30 percent of their value since peaking in June.