Soft German data and downward revisions on Europe's growth forecast by the European Commission, as well as the BoE's reduction of Britain's growth expectations, prompted investors to seek cover in US government debt.

"Part of the bid on Treasuries were related to stock weakness and a little more concern about global growth," said Lou Brien, market strategist at DRW Trading Chicago. "These are old concerns that have resurfaced."

Germany's 10-year bond yields dropped to their lowest level in more than two years, taking a step closer to zero percent, after sharp cuts to the European Commission's growth and inflation forecasts.

Consistently poor German data in recent sessions has raised concerns that Europe's largest economy could tip into recession.

At the same time, British 10-year government bond yields touched an eight-month low after the BoE slashed growth forecasts.

In morning trading, US 10-year note yields fell to 2.673 percent, from 2.704 percent late on Wednesday.

US 30-year bond yields were also down, at 3.016 percent , from 3.038 percent on Wednesday.

On the short end of the curve, US 2-year yields slid to 2.497 percent, compared with Wednesday's 2.524 percent .

Investors are looking to the US Treasury's $19 billion 30-year bond refunding later on Thursday. The rally in Treasuries is offsetting attempts to sell it ahead of the auction.

Investors typically sell Treasuries ahead of an auction to push the yield higher so they can buy them at a lower price.

Three of the last four 30-year refunding auctions have come in higher than market forecast, ranging from 0.2 to 2.3 basis points, which signaled less-robust demand.