The threat of a recession sparked a painful day in US financial markets.
The yield on the closely watched 10-year Treasury fell so low Wednesday that, for the first time since 2007, it briefly crossed a threshold that has correctly predicted many past recessions.
Weak economic data from Germany and China added to recent signals of a global slowdown.
That spooked investors, who responded by dumping stocks, sending the Dow Jones Industrial Average into an 800-point skid, its biggest drop of the year.
The S&P 500 index dropped nearly 3% as the market erased all of its gains from a rally the day before.
Tech stocks and banks led the broad sell-off.
Retailers came under especially heavy selling pressure after Macy's issued a dismal earnings report and cut its full-year forecast.
Investors have been ploughing money into the safety of US government bonds for months amid growing anxiety that weakness in the global economy could sap growth in the US.
Uncertainty about the outcome of the US trade war with China has spurred a return of volatility to the stock market in August, the Dow has dropped more than 5% and the S&P 500 is down more than 4%.
Economic data from two of the world's biggest economies added to investors' fears on Wednesday.
European markets fell after Germany's economy contracted 0.1% in the spring due to the global trade war and troubles in the car industry.
In China, the world's second-largest economy, growth in factory output, retail spending and investment weakened in July.
"The bad news for global economies is stacking up much faster than most economists thought, so trying to keep up is exhausting," Kevin Giddis, head of fixed income capital markets at Raymond James, wrote in a report.
The S&P 500 fell 85.72 points, or 2.9%, to 2,840.60.
The Dow sank 800.49 points, or 3%, to 25,479.42.
The Nasdaq composite lost 242.42 points, or 3%, to 7,773.94.
The Russell 2000 index of smaller company stocks slid 43.05 points, or 2.8%, to 1,467.52.
The losses come a day after stocks rallied when the Trump administration delayed tariffs on about 160 billion US dollars in Chinese goods that were set to take effect on September 1.
President Donald Trump took to Twitter to defend his trade policy Wednesday, saying: "We are winning big time, against China."
But many on Wall Street remain worried that the trade war between the world's two largest economies may drag on through the 2020 US election and cause more economic damage.
"We still see a substantial risk that the trade dispute will escalate further," said Mark Haefele, global chief investment officer at investment bank UBS in a note to clients.
Mr Trump also criticised the Federal Reserve for hamstringing the US economy by raising rates "too much & too fast" last year and not reversing its policy aggressively enough - the Fed cut its key rate by a quarter point last month.