The moves overnight come after U.S. stocks posted their worst two-day stretch in eight months. The three major indexes all fell more than 5 percent between Wednesday and Thursday.
On Thursday, the Dow fell nearly 550 points, bringing its two-day losses to more than 1,300 points. The S&P 500, meanwhile, dropped 2.1 percent and closed below its 200-day moving average for the first time since April.
"Although, it's not really sirens blaring, it's more of a wake-up call," said Mike Loewengart, vice president of investment strategy at E-Trade, about the sell-off. "Fundamentals remain strong and investors should not lose sight of that."
But "with corporate earnings and midterms on the horizon, we could be in store for more turbulence," he said.
October, a month known for major market sell-offs in the past, has been a brutal month for investors so far. The S&P 500 has lost 6 percent during the month so far and is now higher by just 2 percent for 2018.