Markets Around the World Are Rattled by Fears of Slowing U.S. Growth

A sell-off in markets around the world turned into a rout on Monday as investors grew panicky about signs of a slowing American economy, with stocks tumbling across Asia.

The declines were especially pronounced in Japan, where the Topix index, which includes companies that represent a broad swath of the country’s economy, fell 12.2 percent. It was the biggest one-day loss in more than three decades. The decline at one point triggered a “circuit breaker” mechanism that halts trading to let markets digest large fluctuations. The Nikkei 225 index, considered the benchmark in Japan, also fell 12.4 percent.

South Korea’s benchmark Kospi index fell more than 10 percent, triggering its own halt in trading. Equity markets in Taiwan, Singapore, Australia and Hong Kong were all lower.

The declines were expected to continue in Europe and the United States on Monday.

Stock futures for the S&P 500 were down more than 3 percent, and those for the Nasdaq fell 6 percent. Stock futures for key indexes in Europe, including Germany’s, pointed to declines of more than 2 percent.

Bitcoin, a main cryptocurrency, plummeted nearly 14 percent in another apparent sign of investor anxiety.

The drops followed a U.S. jobs report on Friday that indicated that employers had slowed hiring significantly in July, with unemployment rising to its highest level in nearly three years. This deepened fears that the economy was cooling and that the Federal Reserve may have waited too long on cutting interest rates.

Nomura, the Japanese investment bank, said in a research note on Monday that the “slowing U.S. data causes a growth scare for markets,” and that it has “reignited fears of a faster-than-expected U.S. slowdown.”

Based on the weakness in the jobs