The Indian Wells tournament has been cancelled because of concerns about the spread of coronavirus.
The tournament, a combined ATP and WTA event which is one of the biggest and most prestigious outside of the Grand Slams, was due to start this week.
Health officials in California said there was "too great a risk" to hold a "large gathering of this size".
"We are prepared to hold it on another date and will explore options," said tournament director Tommy Haas.
Many of the world's leading players, including men's world number two Rafael Nadal, have already arrived in California for the event.
Qualifying was set to start on Monday with the main draw matches beginning on Wednesday.
The tournament draws more than 400,000 fans each year to Indian Wells, which is 130 miles east of Los Angeles.
The decision to call off the tournament was made after one case of coronavirus was confirmed in the local Coachella Valley area. A public health emergency has been declared by medics.
"It is not in the public interest of fans, players and neighbouring areas for this tournament to proceed," said Dr David Agus, professor of medicine and biomedical engineering at the University of Southern California.
"We all have to join together to protect the community from the coronavirus outbreak."
Coronavirus - a fast-moving infection originating in China - has spread to more than 100 countries and claimed more than 3,800 lives.
"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," added Haas, the former world number two.
WTA chief executive Steve Simon told the New York Times there had been discussions to hold the event behind closed doors but that option was rejected by tournament officials.
What has been the reaction of the players?
Spain's Nadal, 33, was among the first to react to the news, calling the outbreak of the virus "sad".
British doubles player Jamie Murray questioned whether the decision would force other major tournaments to be postponed.
"Doesn't bode well for the tour if Indian Wells cancelled for one confirmed case in Coachella Valley," said the 34-year-old Scot.
British number two Heather Watson set up a vote on her Twitter account asking whether the decision was an "overreaction" or a "good decision".
Belgian player Kirsten Flipkens criticised the WTA for not holding an emergency meeting of the players, with Romanian Sorana Cirstea adding she was only told about the news on Twitter.
Former world number three Pam Shriver, now a leading television analyst, believes it is a "brave, tough but correct decision".
For fucks sake
And now it’s the Fed Cup
The inaugural 12-team Fed Cup Finals have been postponed because of coronavirus.
The event was scheduled to take place at the Laszlo Papp Arena in Budapest from 14 to 19 April.
The Hungarian government banned indoor gatherings of more than 100 people earlier on Wednesday - shortly after the ITF Board had taken the decision to postpone the Finals.
The ITF says it is committed to staging the Finals at a later date this year.
April's play-offs are also affected, which means Great Britain's tie in Mexico has been postponed.