Overnight Dow Jones industrial average futures were down by 183 points as of 2:28 a.m. ET, signaling the October stock market drop that intensified on Wednesday could continue on Thursday. Futures implied the Dow will open Thursday down by 274.74 points.
Overnight S&P 500 futures, for their part, were lower by 0.63 percent and continued to point to a decline at Thursday's open.
The SPDR S&P 500 ETF fell 0.57 percent in after hours trading Wednesday, after falling 3.2 percent during a day which saw stocks sell off throughout the afternoon.
"October weakness intensified today as volume surged and selling was widespread," said Bruce Bittles, chief investment strategist at Baird, in a note after Wednesday's close. "We may need to see evidence of exhaustive selling, increased investor pessimism and a healthier breadth back-drop to suggest that near-term risks are ebbing."
The Dow Jones Industrial Average closed 831.83 points lower at 25,598.74 as Intel and Microsoft fell more than 3.5 percent each. The Nasdaq Composite plummeted 4 percent to 7,422.05 as Amazon and chip stocks declined. It was the worst for the Dow and S&P since February.