China allowed the yuan to breach the key seven-per-dollar level for the first time in more than a decade, in a sign Beijing might be willing to tolerate more currency weakness that could further inflame the trade conflict with the United States.
The decision followed US President Donald Trump's threat last week to impose 10% tariffs on $300 billion of Chinese imports starting Sept. 1.
"There's a lot of fears out there," said Larry Milstein, head of government and agency trading at R.W. Pressprich & Co. in New York. "What is the path that could end this? It doesn't seem we are going to get there anytime soon."
The growing trade friction between the world's two biggest economies appeared to begin hurting the US services sector on top of the squeeze on domestic manufacturers.
The Institute for Supply Management's index on US services activity showed the vast economic sector's growth slowed to its weakest level in three years in July.
Anxious investors have been bailing from stocks and other risky assets with Wall Street's main stock indexes falling 2%.
They have favored US government debt, the yen, gold and other perceived low-risk assets to park their money.
At 10:45 a.m. (1445 GMT), the yields on benchmark 10-year Treasury notes were down 8.8 basis points at 1.7667%. They hit 1.743% earlier on Monday, which was their lowest since Nov. 9 2016, the day after Trump was elected president.
The two-year yield, which is sensitive to traders' view on Fed policy, touched 1.587%, its lowest since November 2017. It was last 11.9 basis points lower at 1.6033%.
Interest rates futures implied traders fully expect the US central bank would lower rates again at its Sept. 17-18 policy meeting after it cut them for the first time since 2008 last week, CME Group's FedWatch program showed.
The difference between the three-month Treasury bill rate and 10-year yields grew to nearly 27 basis points, the widest since April 2007.
This curve "inversion" between the two maturities has preceded every US recession in the past 50 years.
Meanwhile, the blistering demand for Treasuries is expected to stoke bidding for this week's quarterly refunding where the government will sell $38 billion in three-year debt, $27 billion in 10-year notes and $19 billion in 30-year bonds.