The Dow Jones Industrial Average and the broad-based S&P 500 fell about 0.8 percent after a few minutes of trading. The tech-heavy Nasdaq Composite Index lost about 1.5 percent.
Google owner Alphabet fell more than 6 percent. The stock is being pressured by an increased investment plan combined with negative cash flow.
Electric car maker Tesla's stock is falling even more, around 11 percent, after the company reported unexpectedly low profits and increased costs on Wednesday.
Prices are also being pressured by higher oil prices as a result of the crisis in the Middle East.
