"All the key drivers of China's Treasury purchases are disappearing -- there's a waning appetite for dollars and a waning appetite for Treasuries," Ben Simpfendorfer, a Royal Bank of Scotland economist, told The New York Times.

China, surpassing Japan as the No. 1 owner of Treasuries, holds $1 trillion in U.S. debt, the Times said Thursday.

A pullback in purchases, however, could trigger a cyclical rise in interest rates for U.S. borrowers -- currently not an issue as private investors have fled stocks recently in favor of the safe harbor of U.S. Treasuries.

China, however, simply has less money to spend on U.S. debt, due to the global economic slowdown and a downturn in its own stock market, analysts said.

China's export revenues are expected to drop this year.

"The pace of foreign currency flows into China has to slow," said Dariusz Kowalczyk, the chief investment officer at SJS Markets Ltd.

Less money in and a $600 billion domestic stimulus package to pay for means China has less to spend abroad, the Times said.