Chinese shares tumble as G20 ministers gather

Weakness in China, a key driver of global growth, and spasms in the oil market are expected to hang over a two-day meeting of G20 finance ministers in commercial hub Shanghai starting on Friday. The gloomy outlook for the global economy has added to pressure on central bankers to unleash fresh monetary firepower to help stimulate growth and reassure investors. The Shanghai benchmark tumbled 6.41 percent by Thursday's close, while the Shenzhen index on China's second exchange dived 7.34 percent.