Chinese shares tumble 8.5 percent in biggest one-day drop since 2007

Chinese shares tumbled more than 8 percent on Monday as an unprecedented government rescue plan to prop up valuations abruptly ran out of steam, throwing the viability of Beijing's efforts to stave off a deeper crash into doubt.

Major indexes suffered their largest one-day drop since 2007, shattering three weeks of relative calm in China's volatile stock markets since Beijing unleashed a barrage of support measures to arrest a slump that had started in mid-June.

"The lesson from China's last equity bubble is that, once sentiment has soured, policy interventions aimed at shoring up prices have only a short-lived effect," wrote Capital Economics analysts in a research note reacting to the slide.