Stock markets fell further on Monday as investors around the world worried about the health of the American economy and businesses braced for the destabilizing effects of tariffs on global trade.

The S&P 500 fell 1.5 percent at the start of trading on Wall Street, adding to last week’s losses, which were the steepest in several months. After three straight weeks of selling, the index is now about 7 percent below a record set last month, approaching a “correction,” a Wall Street term for a significant decline from a recent high.

The tech-heavy Nasdaq has been hit particularly hard. It fell into a correction last week, and dropped another 2 percent on Monday. Tesla’s shares fell more than 5 percent, Alphabet lost 4 percent and Nvidia slipped more than 2 percent.

Stocks in Europe and Asia also came under pressure. An index tracking the eurozone’s largest public companies, which hit a record high last week, dropped 0.9 percent. Hong Kong’s Hang Seng Index fell more than 1.8 percent.

Investors seeking havens continued to opt for the relative safety of bonds, pushing down the 10-year U.S. Treasury yield to 4.24 percent. (Bond prices move inversely to yields.) The combination of falling stocks and declining interest rates is often seen as a sign of economic unease.

In a Fox News interview that aired on Sunday, President Trump refused to rule out the possibility that his policies would cause a recession.

Over the past few weeks, Mr. Trump has threatened, imposed, suspended and resumed tariffs on America’s largest trade partners: Canada, Mexico and China. The dizzying shifts, including last-minute exemptions for some automakers and energy products, have led to heightened uncertainty, unnerving investors.

“The market volatility is much less about the bad news of tariffs and much more about the uncertainty of tariffs, especially uncertainty as to what the policy is, where it is headed, how long it will last and what the end result will be,” said David Bahnsen, the chief investment officer at the Bahnsen Group.

By most measures, the U.S. economy is still solid, with the latest data on hiring holding steady. But economists have turned gloomier as they come to grips with Mr. Trump’s seesawing approach to tariffs, which have hamstrung businesses trying to plan investments and hiring. Cuts to the federal work force and government spending freezes have also dented consumer sentiment.

Analysts at JPMorgan Chase said in a report that there was a “materially higher risk” of a global recession this year because of “extreme U.S. policies.” They put the probability of such a downturn at 40 percent. Strategists at Goldman Sachs increased the chances of a U.S. recession in the coming year to 20 percent, citing “policy changes as the key risk.”

On Monday, retaliatory tariffs by China on U.S. agricultural products came into effect. On Wednesday, the Trump administration is set to put in place a 25 percent tariff on all steel and aluminum imports. Mr. Trump has also threatened to impose “reciprocal tariffs” on all U.S. imports to match other countries’ tariffs and trading policies next month.