The supply-chain problems have started to affect American homebuilders as well. A senior executive at Toll Brothers said the virus appeared to have delayed the supply of lighting parts.

At the same time, Chinese consumers are buying less. Apple said the closing of stores in China would depress sales of iPhones and other devices.

Mastercard cut its growth forecast in part because people are taking fewer international trips. Fear of the virus has prompted companies like Amazon and Nestlé to suspend international travel by some employees. That drop in demand, combined with their own concerns about the virus, has prompted United and other airlines in the United States and Europe to cancel flights to cities in China and elsewhere in Asia.

On Friday, United said an investor briefing scheduled next week would be postponed until September. Citing concern over the virus, the airline said it “does not believe it is practical to expect that it can have a productive conversation focused on its long-term strategy.”

Companies may also struggle because investors are becoming more reluctant to lend them money. Appetite for new bonds, especially those issued by less-creditworthy businesses, has fallen off. Banks may also have to tighten lending standards. In a sign that investors believe the coronavirus concerns could hit banks hard, the stocks of the three largest U.S. banks — JPMorgan Chase, Citigroup and Bank of America — are all down by a lot more than the S&P 500 so far this year.

Of course, the coronavirus outbreak could end up resembling other brief shocks that have landed only glancing blows on companies and the stock market. These include the fiscal battles of the previous decade that consumed Washington and Wall Street for weeks at a time.