Chinese investors have ignored efforts by the securities regulator to curb downward pressure on the country’s tumbling stock market, with bourses in Shanghai and Shenzhen registering hefty declines on Thursday.

Moves by the China Securities Regulatory Commission late on Wednesday to relax collateral rules on margin loans failed to staunch market losses on Thursday, with the Shanghai Composite Index falling as much as 5.5 per cent — deepening Wednesday’s 5.3 per cent decline — while Shenzhen was down 5.8 per cent.

Margin finance has been a major driver of the rally that propelled China's main stock index to a seven-year high on June 12, but the market has since tumbled more than 20 per cent due in part to worries about a clampdown on leveraged bets.