The drop in yields also reflected a jump in expectations that the Federal Reserve would cut key borrowing costs three more times by year-end
The yuan breached the key 7-per-dollar level for the first time in more than a decade, and President Donald Trump slammed it as "a major violation"
The S&P 500 Index is down 6%
A more comprehensive non-farm payrolls report on Friday is expected to show the economy added 190,000 jobs in December, down from the 228,000 additions in Nov