HONG KONG (AP) — China's main stock benchmark plunged as much as 7 percent Friday as government stabilizing measures failed to reassure panicky investors while other Asian indexes fell ahead of Greece's weekend austerity referendum. The Shanghai Composite Index in mainland China tumbled as much as 7 percent in morning trading but losses moderated by the afternoon, when it was down 3.2 percent to 3,787.91, putting it on track to end the week 16 percent lower. The market rout deepened as investors dumped shares in spite of government measures this week aimed at restoring confidence, such as cutting fees and easing rules on borrowing money for trading. The China Securities Regulatory Commission, the market watchdog, said late Thursday that it's launching an investigation into suspected stock market manipulation, state media reported, in an indication of Beijing's increasingly frantic efforts to halt the market slide.