Bond yields tumbled as comments by US Federal Reserve Chair Jerome Powell and growth data in Europe stoked fear about a global downturn. US stock futures rose slightly following a sharp drop.

The yield on German 10-year bonds slumped as much as 21 basis points, poised for the biggest two-day decline since November 2011, after a report showed economic activity in the euro-area slowed sharply in June.

Contracts on both the US-based S&P 500 and Nasdaq 100 rose after erasing earlier declines.

The Stoxx50 index remained unchanged following a rally of more than 1%

Powell accepted that steep rate increases could trigger a US recession. He said the task of engineering a soft economic landing was "very challenging" in testimony to the Senate Wednesday. Policymakers are taking drastic steps to cool inflation at a four-decade high, and the Fed chair repeated his resolve to get consumer price growth back down to the 2% target.

"The reaffirmation of the Fed's commitment to bringing inflation down and that recession is a risk are adding to growth worries, which is the dominant fear again," Esty Dwek, chief investment officer at Flowbank SA, said.

Traders are now debating how far the Fed will stretch its rate cycle in the face of an economic downturn. Money markets indicate diminished odds the central bank will raise rates beyond year-end, and rising odds of a rate cut from May 2023.

What to watch this week:

• Powell US House testimony, Thursday
• US initial jobless claims, Thursday
• PMIs for eurozone, France, Germany, UK, Australia, Thursday
• ECB economic bulletin, Thursday
• US University of Michigan consumer sentiment, Friday
• RBA's Lowe speaks on panel, Friday