Investors talk in front of an electronic board showing stock informations at a brokerage house in Kaifeng, Henan Province.

China's securities regulator has relaxed rules on using borrowed money to speculate on stock markets, the latest in a flurry of government measures aimed at stemming two weeks of panic selling that is posing a growing risk to the world's second-largest economy.

Just a few weeks ago, authorities were cracking down on riskier margin financing, which had helped Chinese markets more than double in a year.