The yield on the benchmark 10-year Treasury note sat at 2.0443 percent after closing at 2.084 percent on Thursday. It hit a session low of 2.0278 percent, incing closer to the 2 percent level.
The yield on the 30-year Treasury bond was lower at 2.7327 percent, after closing at 2.752 percent.
The yield on the two-year note was at 0.62 percent.
Along with Fed concerns, weakness in China is putting pressure on U.S. equities. Thursday saw stocks slammed in the worst trading day in 18 months, and investors sought safety in bonds, fearing a meltdown in emerging markets currencies and commodities is signalling a broader global malaise.
In Asia, Friday saw China's sharp selloff continue: the Shanghai Composite slid 4.3 percent after disappointing PMI data for August.
On Thursday the Treasury Department auctioned $16 billion of five-year Treasury Inflation-Protected Securities (TIPS) to record investor demand, according to Reuters, with participants enticed by the sector's recent rout.
In oil markets, this week saw U.S. crude hit a new six-and-a–half-year low after falling under $40 a barrel.
CNBC's Patti Domm contributed to this report