Airlines are slashing flights and freezing hiring as they experience a sharp drop in bookings and a rise in cancellations in the face of the spreading coronavirus.

Southwest Airlines CEO Gary Kelly says the outbreak might be worse for airlines than the terror attacks of 2001. An industry trade group believes it will be more damaging.

Delta Air Lines said Tuesday that travel demand has fallen so badly in the past week that it expects one-third of seats to be empty this month on flights within the United States, which was insulated from virus fallout for a time.

United Airlines expects to lose money in the first quarter for the first time in six years.

Business travelers are grounded as meetings and conferences are canceled. Leisure travelers are scared.

Normally airlines try to lure reluctant travelers by cutting fares, but that won’t work with the COVID-19 outbreak.

“If you are scared of flying, you are probably scared at any price,” said Delta President Glen Hauenstein.

Delta, the world’s biggest airline by revenue, said net bookings declined 25 percent to 30 percent in the past two weeks and could get worse. It will cut international flights by 20 percent to 25 percent and reduce U.S. flying by 10 percent to 15 percent roughly matching cuts previously announced by United Airlines.

Delta is also cutting spending, putting a freeze on hiring, offering voluntary unpaid leave, delaying voluntary pension contributions and suspending share buybacks.

American Airlines announced it will cut international flying by 10 percent this summer and reduce U.S. flying by 7.5 percent in April. It has delayed training of new pilots and flight attendants.

United arranged $2 billion in additional bank credit to raise liquidity from $6 billion to $8 billion. President Scott Kirby said United hopes the outbreak won’t be as damaging as 9/11, when bookings plunged 40 percent for two months before starting to recover, “but we’re not willing to count on that.”

Kirby and United CEO Oscar Munoz will waive their base salaries through June, and Kelly, the Southwest CEO, said he will take a 10 percent pay cut.