Like a bear in a China shop

China's stock market has cooled off on renewed fears of a hard economic landing. But U.S. stocks continue to sizzle. How much longer can that last if China's growth does slow？

NEW YORK -- Contact lenses, diamonds and boiled eggs are things that are better hard than soft. But economic landings in China? That's a different story. There are increasing concerns that China's economy, while still growing at a pace that's the envy of just about every other nation, may cool off more quickly than hoped. Chinese stocks have been crushed in the past few days as a result.

The Shanghai Composite (SHCOMP) is down more than 5% in just the past five days and is now up only about 2% year-to-date. That lags the gangbuster performance of the U.S. stock market this year. But China's market had been rising in tandem with the S&P 500 (SPX) until the hard landing fears cropped up.

Shares of Chinese companies that trade in the United States have suffered too. Industry leaders Aluminum Corp. of China (ACH), China Eastern Airlines (CEA), China Telecom (CHA) and oil company CNOOC (CEO) are just a few examples of Chinese companies that have tumbled in the past few days.

Is there reason to be worried? Yes. The latest reading on manufacturing in China was weaker than expected. In addition, key companies in important sectors in China have been reporting disappointing earnings lately. And that's really spooked the global markets. After mining company Jiangxi Copper reported a drop in earnings Wednesday, copper prices fell more than 2%.

Demand for copper is often viewed as a telling predictor of economic growth as the commodity has a wide array of industrial and manufacturing uses. This relationship has even earned the red metal the nickname Dr. Copper among traders, in that copper has a PhD in economics.