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

The unprecedented move 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.

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

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

For most people, the 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, most coming from a television contract with CBS and Turner that pays the NCAA almost $800 million US per year.

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. The NCAA women's tournament began in 1982 and it, too, has become a big event, raising the profile of the sport.

"I'm disappointed but I totally understand. I really feel for the senior student-athletes; every student-athlete, but particularly the seniors because this is their last chance for the fans," said Oregon women's coach Kelly Graves, whose team would have entered the tournament as favourites to reach the Final Four in New Orleans. "There's something more important than the games going on. I've kind of come to grips to that a little more than a few hours ago."

Games would have started on the men's side on Tuesday in Dayton, Ohio, before spreading out to eight sites from coast to coast from next Thursday through Sunday. The women's tournament was scheduled to begin March 20, with first- and second-round games to be played at 16 sites on or near the campuses of the top teams.

The men's Final Four was to be played April 4 and 6 at Mercedes-Benz Stadium in Atlanta. The semifinals and final typically pack football stadiums for the games, and after the champion is crowned the best moments of the year's tournament are wrapped up into the "One Shining Moment" montage that has become a staple of CBS' television coverage through the years.