From Las Vegas to Macao and Monte Carlo to Sydney, gambling magnates are luring more Chinese their way. Gambling, you see, is illegal in the Chinese mainland. Then again, who needs baccarat tables and roulette wheels when you have China's stock market?

China's equity exchanges have long had more in common with casinos than markets. Investors were reminded of that on Jan. 31 when China's stocks tumbled the most in at least 21 months after a lawmaker said shares were overvalued. The comments by Cheng Siwei, vice chairman of the National People's Congress, fueled speculation the government will act to limit investment.

Speaking in Dubai, Cheng said only 30 percent of companies listed on the Shanghai Stock Exchange "are good to invest in by Western standards," and investors in the remaining 70 percent will probably lose money. His words sent the Shanghai and Shenzhen 300 Index, which tracks yuan-denominated A shares listed on China's two exchanges, down 6.5 percent, the biggest one-day drop since the measure was introduced in April 2005.

A couple of things are worth considering here. One, when you think about what Cheng said, the biggest surprise is that Chinese stocks didn't fall more. You have to wonder if his 30/ 70 comment is too optimistic given China's lack of corporate transparency and government efforts to slow the economy.

Two, even after the Jan. 31 plunge, this year's gain is still 17 percent. No, that's not a typographical error. If stocks had ended unchanged on that day, they would be up almost 25 percent in little more than four weeks. How is that not a bubble?

"Every investor thinks they can win, but many will end up losing," Cheng was quoted as saying in the Financial Times.

Cheng's comments seem reminiscent of ones by Microsoft's chief executive, Steve Ballmer, in September 1999. After Ballmer, who was company president at the time, quipped that "there's such an overvaluation of tech stocks that it's absurd," markets plunged.

To say "irrational exuberance" has crept into China would make Alan Greenspan's catchphrase seem like an understatement. Just as many investors wished they had heeded Ballmer's warning, bettors may regret not reacting more to Cheng's.

The popping of China's bubble probably won't hurt global markets the way the Nasdaq Composite index's implosion did in 2000. That episode probably has Greenspan, the former Federal Reserve chairman, wishing he had done more than just raise questions about bubbles in the mid-to- late 1990s. Why the Fed didn't try to temper that exuberance will long mar Greenspan's legacy.

You can bet China's central bank governor, Zhou Xiaochuan, is thinking about what he can do to return some sobriety to markets. Whatever China ends up doing, the bubble speaks volumes about the cracks in Asia's No. 2 economy -- and misperceptions about its medium-term outlook.

Legend has it that Joseph Kennedy, father of former U.S. President John F. Kennedy, avoided Wall Street's 1929 crash thanks to a shoeshine boy. Just before the market collapsed, Kennedy received unsolicited stock advice from a young man polishing his loafers. Kennedy, the story goes, got out of the market the next day, figuring stock enthusiasm had run wild.

In the late 1990s, similar omens came from New York taxi drivers and Miami bartenders offering stock tips or bragging about their day-trading gains. One hears such conversations in major Chinese cities these days.

Last month, I sat next to a British hedge-fund manager on a flight from Tokyo to Bangkok. The day before, while in Shanghai, he was buying DVDs from a salesman who said with a wink: "If you don't own Tsingtao Brewery stock, you should get in now." The hedge-fund manager, who refused to be quoted by name, called it his "Joe Kennedy moment."

The Shanghai and Shenzhen 300 Index has more than doubled in the past 12 months as government efforts to make more than $200 billion of state-owned stock tradable revived investor demand. Economic growth that has averaged 10 percent for the last five years also helped increase companies' earnings.

China doesn't need more money rushing into its markets. It needs more mature markets, better transparency and more efficient mechanisms. That explains why China's potential with institutional investors is yet to be fulfilled while the nation of 1.3 billion pulls in most of the world's foreign direct investment.

Officials in Beijing and Shanghai should consider something else Ballmer said in 1999, at the peak of the U.S. stock bubble. He said such high stock valuations are "bad for the long-term worth of the economy."

One can argue that after a long period of lackluster performance, China's share markets are playing catch-up. Yet the idea that a multiyear rally in Chinese shares is afoot lacks support from the underlying economy.

Chinese stocks may one day be a stellar investment. At the moment, they seem more like the casinos that Chinese law forbids.