The comments from China's premier Wen were unusually pointed and raised the possibility that Beijing's appetite for U.S. debt could wane. In the worst-case scenario, a significant new aversion to U.S. investments could drive down the dollar and drive up interest rates, worsening the U.S. recession. Mr. Wen indicated China wouldn't be rash in making changes to its $1.946 trillion stockpile of foreign reserves. While China is looking out for its own interests, it will "at the same time also take international financial stability into consideration, because the two are inter-related," he said.

"We have lent a huge amount of money to the U.S., so of course we are concerned about the safety of our assets," Mr. Wen said in response to a question at his annual news conference. "Frankly speaking, I do have some worries."

Mr. Wen said China alone would decide where the yuan goes from here. "No country can pressure us to appreciate or depreciate" the currency, he said.