Wall Street was headed for a second day in the red on Thursday as US stocks opened lower on revived worries for global growth.
The European Commission on Thursday slashed its 2019 growth forecasts as difficulties in Germany, Italy and France mount.
Investors were also absorbing continued quarterly earnings reports and the news of a planned $66bn bank merger between BB&T and SunTrust, creating the sixth-largest US bank.
Ten minutes into the day's trading, the blue-chip Dow Jones Industrial Average was down 0.7%, or nearly 170 points, at 25 209.46.
The broader S&P 500 was 0.8% lower at 2 709.95 while the Nasdaq had fallen 1% at 7 300.09
Stocks have risen steadily this year, recovering from December's rout as investors expressed relief at signs the Federal Reserve is likely to pause its interest rate increases while Beijing and Washington work toward resolving their trade war.
But analyst Patrick O'Hare wrote at Briefing.com that in the interim "the view has gotten a little cloudier, with valuation concerns re-entering the trading mix."
BB&T jumped 5% while SunTrust soared 11% following the announcement of the merger, which is expected to close in the fourth quarter of this year, subject to ratification by shareholders and regulatory approvals.
Twitter nose-dived 10.8% after quarterly results showed higher profits but a shrinking global user base.
Fast-food purveyor Yum! Brands sank 2.2% following disappointing earnings.