WASHINGTON — The number of Americans seeking unemployment aid rose last week to 742,000, the first increase in five weeks and a sign that the resurgent viral outbreak is likely slowing the economy and forcing more companies to cut jobs.

The worsening pandemic and the arrival of cold weather could accelerate layoffs in the weeks ahead. Of the roughly 20 million Americans now receiving some form of unemployment benefits, about half will lose those benefits when two federal programs expire at the end of the year.

“The risk of further job and income loss is high now from business operations being curtailed,” said Rubeela Farooqi, chief U.S. economist at High Frequency Economics, a forecasting firm. “Also, expiration of federal benefits later this year will put renewed strain on household incomes. Overall, the labor market remains under stress.”

The Labor Department’s report Thursday showed that applications for jobless aid rose from 711,000 in the previous week. In March, when the pandemic first intensified, the number had soared to 6.9 million. Before then, applications typically hovered about 225,000 a week.

The surge in confirmed viral infections, and worry about its effect on the economy, are putting pressure on financial markets. The Dow Jones Industrial Average declined in early trading Thursday for a third day.

The economy’s modest recovery is increasingly at risk, with newly confirmed daily infections in the United States having exploded 80 percent over the past two weeks to the highest levels on record. More states and cities are issuing mask mandates, limiting the size of gatherings, restricting restaurant dining, closing gyms or reducing the hours and capacity of bars, stores and other businesses. At least 15 states have tightened curbs on businesses to try to slow infections.

Evidence is emerging that consumers are losing confidence in the economic outlook and pulling back on shopping, eating out and other activities. Spending on 30 million credit and debit cards tracked by JPMorgan Chase fell 7.4 percent earlier this month compared with a year ago. That marked a sharp drop from two weeks earlier.