United Airlines will cut domestic flights by 10 percent and international flights by 20 percent next month, and executives are planning “similar reductions” in May, the airline said Wednesday, underscoring the drop-off in demand for air travel given the worldwide spread of the coronavirus. JetBlue also announced some cuts.

Many major U.S. firms have paused nonessential travel, scientific conferences have been canceled, and some would-be passengers have balked at flying during a time of high uncertainty.

“We sincerely hope that these latest measures are enough, but the dynamic nature of this outbreak requires us to be nimble and flexible moving forward in how we respond,” United chief executive Oscar Munoz and President J. Scott Kirby said in a statement.

The airline is seeking volunteers at the company to take unpaid leaves of absence and is instituting a hiring freeze “except for roles that are critical to our operation,” the executives said, noting that management and administrative salary increases are also being delayed.

United said that “given the high level of uncertainly regarding travel,” no change fees will be charged for any domestic or international tickets purchased between March 3 and March 31.

United pointed to sharp cutbacks in flights by other airlines, saying that Cathay Pacific “had canceled more than three-quarters of its weekly flights in March,” and British Airways is making deep cuts later this month given the “large decline” in ticket purchases.

On Wednesday, JetBlue said in a statement that it would reduce capacity by “approximately 5% in the near term to address a fall in demand.” The company said it would monitor booking trends to see whether additional reductions are needed.

JetBlue said it was also taking other steps to preserve cash, including “reducing hiring for both frontline and support center positions, considering voluntary time off programs as appropriate, and limiting non-essential spending.”

 “Airlines are experiencing double-digit declines in demand, and on many routes traffic has collapsed,” Alexandre de Juniac, director general of the International Air Transport Association, said in a statement. The group noted that China’s Transport Ministry “reported an 80% annual fall in volumes in late January and early February.”

Globally, travel demand still rose 2.4 percent in January, compared with the same period the year before, the group said. Those figures only partially reflected the impact of travel restrictions, some of which did not begin until late January, the group said. Still, it marked the lowest increase in demand for travel since April 2010, during “the volcanic ash cloud crisis in Europe that led to massive airspace closures and flight cancellations.”

Travel in December, by contrast, was up 4.6 percent from the previous year. The signs of slowdown reflect the “tip of the iceberg in terms of the traffic impacts,” de Juniac said.

The U.S. Travel Association reiterated that the outbreak is “expected to disrupt inbound travel, particularly from fast-growing Asian markets, over the coming months.”

United is cutting back flights to Asia and suspending its trips to Hong Kong, Beijing, Shanghai and Chengdu, in Sichuan province.

United said its “aggressive” actions are designed to minimize impacts as much as possible, for example by cutting the weekly frequencies of certain flights, targeting routes that have alternatives “via other United hubs,” and delaying the start of seasonal travel. The airline said it would not completely cut off flights to any of its domestic destinations.

United said the specific schedule changes would be made public Saturday.

Clarence Williams contributed to this report.