The aviation industry was already grappling with the worldwide grounding of Boeing’s 737 Max, which has been out of service for a year after two deadly crashes. Losing that one plane sapped some airlines of expected growth, forced them to cancel thousands of flights and resulted in billions of dollars in losses.

The more fundamental issue posed by the coronavirus — that large swaths of the traveling public may simply stay off planes for the foreseeable future — is a far greater threat. Though still in its early stages, there are concerns that a prolonged disruption could do lasting economic damage. Commercial aviation, like the internet, is part of the connective tissue of the global economy.

“In little over two months, the industry’s prospects in much of the world have taken a dramatic turn for the worse,” said Alexandre de Juniac, head of the International Air Transport Association, which forecast the potential revenue drop of more than $100 billion. The rapid shift in fortune is “almost without precedent,” he said.

Around the world, there were signs that global air travel was increasingly grinding to a halt. On social media, travelers shared images of planes devoid of passengers. Others posted photos of empty airports and tarmac workers wearing full-body protective gear in major hubs like New Delhi, Zurich and Istanbul.

Kristi Faulkner, president of Womenkind, an advertising agency, said she was planning to attend Shoptalk, a major conference for retail brands, in Las Vegas. On Thursday, when the conference was postponed, Ms. Faulkner tried to call Delta Air Lines, but a message informed her that there was a three-hour wait to speak to a representative. If she was not traveling in the next 72 hours, the message said, she should call back another day.

“How could they not be prepared for an onslaught of concerned travelers?” she asked. “The phone lines are jammed.”

Dolly Meckler, a social media strategist, flew from New York to Los Angeles on Wednesday after taking meetings and visiting family. “Half my flight was empty,” she said, noting that many passengers were using wipes to disinfect their seats. “A lot of us in the main cabin had our own rows.”