The NCAA canceled its men’s and women’s basketball tournaments today because of the spread of coronavirus, putting an abrupt end to the season less than a month before champions were to be crowned.

The decision comes a day after the NCAA announced the games that were scheduled to start next week would go on, but played in mostly empty arenas. That plan was scrapped as every major American sports league from the NBA to MLB put the brakes on its season due to concerns about the pandemic.

The NCAA canceled all of its spring championships in every sport, which include hockey, baseball and lacrosse.

For most people, the new coronavirus causes only mild or moderate symptoms, such as fever and cough. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia. The vast majority of people recover from the virus.

The NCAA men’s basketball tournament has been played every year since 1939 when Oregon won the championship in Evanston, Ill. It has grown through the years, both in size and stature. The three-week tournament generates almost a billion dollars in revenue each year for the NCAA and its hundreds of member universities and colleges.

It is now one of the biggest events in American sports, a basketball marathon of buzzer-beaters, upset and thrills involving 68 teams. The field for the men’s tournament was scheduled to be announced Sunday. The 64-team women’s field was to be revealed Monday.

Games would have started on the men’s side on Tuesday in Dayton, Ohio, then spreading out to eight sites from coast-to-coast from next Thursday through Sunday.

Instead, March Madness had taken on a different meaning as sports have virtually shutdown.

“This decision is based on the evolving COVID-19 public health threat, our ability to ensure the events do not contribute to spread of the pandemic, and the impracticality of hosting such events at any time during this academic year given ongoing decisions by other entities,” the NCAA said in a statement that referred to the illness.

Although the NCAA’s president, Mark Emmert, said in an interview Wednesday evening that he thought the limits on fan attendance had left the association in “the right place,” he declined to rule out the possibility of an outright cancellation. Within 24 hours, mounting fears — and a wave of conference tournament cancellations — led the association to scratch the national competitions.