As the economic impact of the coronavirus outbreak ripples out from the epicenter in China, airlines have been among the hardest hit.

Already, the outbreak is leading to sharp reductions in air travel demand in the US, with major companies such as Amazon ordering a freeze on all non-essential employee travel. The result is clear in photos showing empty airplane seats and deserted terminals.

In China, the impact has been even more severe, with air travel plummeting 80 percent at the country's busiest airports and mass cancellations of both domestic and international flights.

The reduction in global airline capacity, measured by how many seats remain grounded, is now greater than after the terrorist attacks of September 11, 2001, industry analysts say.

After 9/11, airline revenue dropped an estimated $19.6 billion in 2002 dollars. The coronavirus crisis could cost the industry an estimated $29.3 billion in lost revenue for 2020, according to the industry group IATA.