Most investors are aware of the elevated levels of government debt across the developed world, most notably in the eurozone periphery, the U.K., the U.S., and Japan. But fewer recognize that even China is vulnerable to an explosion in debt.

Chinese corporations, local governments, and state-owned enterprises have piled on alarming levels of debt over the past five years. So far, large-scale defaults have been avoided, largely because China's banks have decided to roll over a large number of these loans. But for how long can this practice continue?

Chinese firms continue to pile on debt
According to GK Dragonomics, a China-based economic research firm, indebtedness among the country's corporations soared from an already alarming 108% in 2011, to 122% last year, the highest level in at least 15 years.

This data illustrates a dangerous trend that has been unfolding among the nation's companies. Faced with slowing growth and tighter margins, Chinese corporations have responded by taking on more debt -- a course of action that could lead to a disastrous end game.

The examples of heavily-indebted Chinese firms are countless. Yingli Green Energy Holding Co Ltd (NYSE: YGE), the third-largest solar-panel maker in the world, has languished at the hands of colossal losses and a plunge in the prices for its products. Yingli's stock has collapsed from its late-2007 high of nearly $40 a share to less than $3 a share  currently.

You'll note that the company is listed on the New York Stock Exchange. Now, if Yingli were a U.S. firm facing those same difficulties, you'd think it was just a matter of time before it filed for Chapter 11 bankruptcy (unless, of course, it was too big to fail). But not in this case.

China's state-owned banks keep spoon-feeding credit -- at below-market rates, nonetheless -- to the unprofitable solar-panel manufacturer. Since 2009, Yingli's outstanding short-term loans have nearly tripled.  Unfortunately, the solar company isn't an isolated case. Rather, it's a microcosm of the state of China's corporate sector.

Chinese corporate indebtedness and overcapacity
Reuters recently surveyed 40 of China's most indebted corporations and found that the majority of them were in sectors that are burdened by gross overcapacity. The news agency's analysis unveiled a dangerous combination of soaring debt levels and falling profits among the 40 firms, which included Xinjiang Goldwind Science & Technology Co Ltd, a manufacturer of wind turbines,  and COSCO Shipping Co Ltd.

Overcapacity, which more and more commentators are recognizing as a serious flaw in China's economy, appears to be getting worse. Important industries, such as aluminum, coal, construction, and steelmaking, continue to be burdened by excess capacity and shrinking margins. But, instead of reducing capacity -- as rational economic motives would dictate -- they continue to expand. The reason?

Many of them have been instructed by the central government to continue increasing capacity. Helen Lau of UOB Kay Hian , the largest listed securities firm in Singapore, explains:

All the big producers have strong backing from the state banks. That is why they have been adding new capacity. This is not a commercial decision but a political one.

There you have it. It's a government decision, not an economic one. According to Lau, China's largely state-owned steel industry is 200 millions tons over capacity . Yet, it shows no signs of slowing down. Where will all the steel go? To construct ever more high-rise apartments that nobody will live in?

When in debt, roll over
The big question now is how all this debt will be repaid. On the face of it, China is no different from Western economies like the U.S. and those in the peripheral eurozone, which racked up tons of debt during economic boom years, only to be faced with the seemingly insurmountable challenge of reducing it during a period of slow global economic growth.

But upon closer inspection, it appears that China's debt has grown much faster in the five-year period since 2008  than debt in either the U.S. or the eurozone periphery in the five years leading up to those regions' respective crises. All other things being equal, this would suggest that China's downturn -- if there is one -- could be much more severe.

Though only time will tell, I suspect that a meaningful percentage of recently-issued Chinese loans will eventually turn sour. When? That's tough to say. The issue hasn't come to the surface yet, because the country's banks, instructed by the central government, continue to roll over debts. Faced with a ton of loans coming due within the next couple of years, they have decided simply to extend loan maturities as a way of delaying repayment and avoiding large-scale defaults.

While some commentators are confident that debt-financed investments launched in recent years will easily generate a rate of return above their cost of financing, skeptics have issued warnings that the practice of rolling over loans will end badly. They suggest that it will continue adding to banks' bad loans, while keeping their overall balance sheet quality favorably disguised. Eventually, they argue, it could jeopardize the entire banking system's liquidity.

According to Zhang Zhiming , head of China research at HSBC:

If lenders stopped rolling over debt, everyone would have trouble. Then, there would be a chain reaction and there will be a systemic risk.

Final thoughts and ways to invest in China
While large-scale debt rollovers may be an adequate short-term solution, the practice is clearly unsustainable, and must eventually come to a head. As Herbert Stein, chairman of the Council of Economic Advisers under Richard Nixon and Gerald Ford, famously said, "If something can't go on forever, it won't."

That's not to say there aren't Chinese stocks worth considering. Many investors have turned their attention to Chinese technology stocks, often predicated upon the premise that the nation's growing middle class presents tremendous opportunity for this sector. The number of Chinese Internet users swelled to 538 million last year, according to the China Internet Network Information Center, while penetration levels remained relatively low at 40%.  

Many suggest that the growing number of Chinese Internet users, projected to rise to 800 million by 2015 according to one estimate , should provide a catalyst for companies like Baidu (BIDU -0.09%), China's largest search engine, SINA (SINA), which offers services similar to Twitter, and Youku Todou (NYSE: YOKU), which offers video content similar to YouTube.

Though Baidu and SINA shares took a hit after reporting third quarter earnings that offered gloomy  projections, including a sequential decline in revenue for the fourth quarter, Youku  Todou saw an immediate surge following its third quarter earnings report, as it projected much higher revenue for the fourth quarter than the consensus estimate.

While these companies no doubt face their share of challenges, they may be worth investigating further based upon favorable long-term trends like the projected growth in Chinese Internet and smartphone users over the next few years.