ap photo Yvette Arrington, with the New York Stock Exchange Trading Floor Operations, works on the floor of the NYSE, Monday.

WASHINGTON — A gyrating stock market is seizing headlines as the coronavirus threatens corporate profits and economic growth. Yet it’s in the normally temperate bond market, where companies go to borrow money, where the gravest dangers may lurk.

Investors fear that businesses that have borrowed heavily, especially energy, airline and cruise line companies, will struggle to pay their debts as customers cancel trips and hunker down at home. The shutdown of normal business is shrinking demand for energy in particular, sending oil prices sinking and intensifying pressure on indebted oil-and-gas production firms.

The numbers are enormous.

Having binged on borrowing, companies that are outside the financial sector owe $9.6 trillion in the United States — up more than 50% in a decade. Worldwide, companies have issued $13 trillion in bonds, according to the Organization for Economic Cooperation and Development. That’s twice what they owed in the financial crisis year of 2008. Corporate debt in China alone has soared from virtually nothing to $590 billion.

Add in what companies owe banks and other creditors, and their debts come to $75 trillion worldwide, up from $32 trillion in 2005, the Institute of International Finance says.

Struggling to meet debt payments under the pressure of a virus-induced economic slump, companies are more likely to lay off workers, delay investments and cut costs. All of which could deepen any economic downturn.

Still, optimists note that banks are far healthier than they were in 2008, when millions of homeowners were saddled with mortgages they couldn’t pay. And central banks are striving to limit the damage. The Federal Reserve has stepped up its daily short-term lending to help businesses meet short-term financing needs such as meeting payrolls.

“I don’t think we have anything shaping up like 2008 or 1929, particularly in the United States,” said Kenneth Rogoff, a Harvard economist who has written about the history of financial crises.

Over the past decade, though, companies have borrowed heavily to capitalize on record-low rates. Many have used the proceeds not to hire or expand but to issue dividends to shareholders or to buy back their own stock.