Several players took to social media to claim they hadn't been informed of the cancellation, instead forced to find out online themselves.
Sorana Cirstea and Kirsten Flipkens were among those frustrated voices. An hour before the decision was made, Flipkens wrote: "We know nothing so far."
When the cancellation was confirmed, she tweeted "what the f***?!?!?!" before openly criticising the WTA.
The Riverside County Public Health Department declared a public health emergency for the desert cities 177km east of Los Angeles, including Indian Wells where the ATP and WTA tours were to play the two-week tournament.
Governor Gavin Newsom has declared a state of emergency. California has reported 114 cases of the virus.
"There is too great a risk, at this time, to the public health of the Riverside County area in holding a large gathering of this size," Dr David Agus, professor of medicine and biomedical engineering at the University of Southern California, said on Sunday. "It is not in the public interest of fans, players and neighbouring areas for this tournament to proceed. We all have to join together to protect the community from the coronavirus outbreak."
The event typically draws upwards of 450,000 fans. It is commonly referred to as the "fifth slam" because of its popularity among the players and its stature, ranking points and over $27 million (US$17m) in prize money that place it one rung below tennis' four Grand Slam tournaments. This year's field included Nadal, Novak Djokovic, Serena Williams, Naomi Osaka and Coco Gauff. Kim Clijsters was set to continue her comeback at the event.
"So sad to hear the news about the postponing of @BNPPARIASOPEN," Gauff tweeted. "I was so excited to make my debut in IW, but safety is always the No. 1 priority. Stay safe."
Tournament director Tommy Haas said organisers are prepared to play the event on different dates and will explore options. However, the pro tennis calendar is tightly scheduled and the summer months in the desert are notoriously hot.
"We are very disappointed that the tournament will not take place, but the health and safety of the local community, fans, players, volunteers, sponsors, employees, vendors, and everyone involved with the event is of paramount importance," Haas said in a statement.
Already some smaller tennis events in China and Italy - the two countries hardest hit by the virus - had been affected. The Miami Open, which follows Indian Wells later this month, could be in jeopardy. The Ultra music festival in that city has already been cancelled. The year's second Grand Slam tournament, the French Open, is set to be played in Paris in May.
Refunds for this year's event or a credit toward next year's tournament are being offered.
Meanwhile, a charity event featuring Nadal set for Tuesday night at Indian Wells Tennis Garden has also been cancelled, tournament spokesman Matt Van Tuinen said.
Nadal was set to be joined by defending BNP Paribas Open champion Dominic Thiem, Daniil Medvedev, Matteo Berrettini, Stan Wawrinka, Milos Raonic and American Taylor Fritz for the Eisenhower Cup, a $235,560 (US$150,000) winner-takes-all event.
Earlier in the week, officials had announced several measures to protect players, fans and staff at the tennis tournament.
Ball kids were going to have to wear gloves and not touch the towels of players on the court. Organised player and fan interaction was also going to be limited at the tournament. Besides ball kids, restaurant and food supply workers were going to wear gloves as well as volunteers taking tickets at entrances. Over 250 hand-sanitising stations were set up throughout the venue.
Other major sports and entertainment events in the desert are scheduled for next month.
The LPGA Tour is to play the first women's golf major of the year, the ANA Inspiration, on April 2-5 in Rancho Mirage.
The Coachella Valley Music and Arts Festival in nearby Indio is set for April 10-12 and April 17-19. It typically draws 250,000 people over two weekends. The Stagecoach Festival, featuring country music, is scheduled for April 24-26 at the same Indio venue.
- AP
