Asia has a China problem. Beijing has just initiated its biggest cut in bank reserve requirements since 2008, a move that underscores just how worried it is about its economy. But the cut is also a stark wake-up call for neighbors that have gotten used to riding China's boom. For years, China's steady growth served as a welcome antidote to an otherwise gloomy global scene. Now even China is sputtering in ways that should worry officials from Seoul to Jakarta.

The People's Bank of China betrayed a sense of heightened anxiety this week. Normally, the central bank tweaks the amount of cash lenders must set aside as reserves by 50 basis points, at most. Slashing it by 1 percentage point leaves little doubt that, amid a collapse in the price of commodities like iron ore (down 30 percent this year), China is decelerating faster than President Xi Jinping had expected.

What's more, the contradictory signals coming out of Beijing suggest policy makers are at odds over how to respond. The PBOC's cut — which will allow banks to add $194 billion of new lending to the economy — came two days after the China Securities and Regulatory Commission clamped down on margin trading to curb froth in the stock market. Even as Beijing has been warning its 1.3 billion people not to bet too heavily on stocks, it has been loosening rules to allow investors to open as many as 20 trading accounts.