US stocks started the day lower on Thursday after the Federal Reserve met expectations with a 50 basis point interest rate hike. 

Interest rate concerns escalated after the European Central Bank quickly followed up the Fed's move with its half-point rate hike.

Investors were still swallowing Wednesday's FOMC meeting, which tackled the central bank's outlook for 2023. Fed Chair Jerome Powell said that future rate hikes could end up being higher than previously thought despite a better-than-expected inflation report on Tuesday. 

"Economic data and the Fed are clearly signaling a new stage of decelerated tightening," said Ron Temple, chief market strategist at Lazard. "For investors, that doesn't mean smooth sailing ahead."

On Thursday, ECB chief Christine Lagarde echoed the Fed's plans, saying that interest rates in Europe will remain high because inflation has yet to be tamed in a convincing manner. She said keeping interest rates higher will "guard against the risk of a persistent upward shift in inflation expectations" and added that future rate hikes will still by "data dependent."  

Here's where US indexes stood shortly after the 9:30 a.m. opening bell on Thursday: 

• S&P 500: 3,948.65, down 1.17% 

• Dow Jones Industrial Average: 33,648.38, down 0.94% (317.97 points)

Nasdaq Composite: 11,018.10, down 1.35%