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Analysis: Your guide to understanding the yuan-dollar currency spat
Foreign speculators are betting the yuan is going to rise like Amazon.com stock in the 1990s. So they're rushing into China to buy the yuan at 15 cents a pop, hoping to sell it later when the price is, say, 17 cents, pocketing two cents per yuan profit. Sounds like chump change, but it adds up if you're swapping large amounts.
Meanwhile, speculators are parking their yuan in Chinese property. That's driving a massive property bubble, particularly in places like Shanghai. The country's in the grip of a speculative "mania," warns Xie, and "the day of reckoning will come."
He thinks "hot money" accounts for fully half of China's accumulated reserves.
UBS' Wang isn't as worried. She admits some speculators have bet on the yuan, especially since 2007. But she says China still keeps close tabs over foreign money flows, and has many controls. "It's not so easy to get in and out," she says.
That means small speculators may be able to move money back to the home country. But big institutional investors that could really distort China's currency market can't move money in and out of China the way they can in some other countries, says Wang.
Her investment house's latest estimate is that "hot money" accounts for less than 20 percent of China's accumulated reserves, or $480 billion at most.
So who's right?
Ask your nearest economist. And expect to hear three different answers.
This story was updated to add details of Monday's meeting between President Barack Obama and Chinese President Hu Jintao.