Stocks fell sharply on Wall Street on Friday amid a fresh escalation of trade tensions between China and President Trump, pushing the market to its fourth straight weekly loss.

The S&P 500 dropped more than 2.5 percent, and the Dow Jones industrial average and technology-heavy Nasdaq index experienced similar declines.

Investors were on edge even before trading started after China vowed to answer the Trump administration’s next round of tariffs on Chinese goods by increasing tariffs on American imports. Around 11 a.m., Mr. Trump fired back with a series of messages on Twitter.