Mr. Wen spoke out in an attempt to change the course of an economy dangerously dependent on one lever to generate growth: heavy investment in the roads, factories and other infrastructure that have helped make China a manufacturing superpower. Then along came the 2008 global financial crisis. To keep China’s economy growing, panicked officials launched a half-trillion-dollar stimulus and ordered banks to fund a new wave of investment. Investment has risen as a share of gross domestic product to 48%—a record for any large country—from 43%. …

Since 2008, China’s total public and private debt has exploded to more than 200% of GDP—an unprecedented level for any developing country. Yet the overwhelming consensus still sees little risk to the financial system or to economic growth in China. …

On the most important measures of this rate, China is now in the flashing-red zone. The first measure comes from the Bank of International Settlements, which found that if private debt as a share of GDP accelerates to a level 6% higher than its trend over the previous decade, the acceleration is an early warning of serious financial distress. In China, private debt as a share of GDP is now 12% above its previous trend, and above the peak levels seen before credit crises hit Japan in 1989, Korea in 1997, the U.S. in 2007 and Spain in 2008.

Even if China dodges a financial crisis, then, it is not likely to dodge a slowdown in its increasingly debt-clogged economy. Through 2007, creating a dollar of economic growth in China required just over a dollar of debt. Since then it has taken three dollars of debt to generate a dollar of growth. This is what you normally see in the late stages of a credit binge, as more debt goes to increasingly less productive investments. In China, exports and manufacturing are slowing as more money flows into real-estate speculation. About a third of the bank loans in China are now for real estate, or are backed by real estate, roughly similar to U.S. levels in 2007.