© issei kato/Reuters

TOKYO—Japanese Prime Minister Shinzo Abe said he agreed with the International Olympic Committee’s president that the Summer Olympics previously scheduled to start in Tokyo on July 24, 2020, would be delayed by around one year.

Mr. Abe spoke by phone Tuesday with IOC President Thomas Bach.

Citing the spreading coronavirus pandemic, the Japanese leader said it was difficult to hold the Olympics this year and a delay was needed to ensure the safety of athletes and spectators. He said he proposed a delay of “about one year” and received “100% agreement” from Mr. Bach.

“We have agreed that the Tokyo Olympics and Paralympics will be held by the summer of 2021 at the latest,” Mr. Abe said in Tokyo. He said study would now begin on arranging venues for the Games.

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An IOC spokesman said a statement would be coming later Tuesday.

Mr. Abe didn’t give an exact date for the start of the Games in 2021. The Olympics originally were scheduled to run July 24 to Aug. 9.

The decision to postpone an event as massive, expensive and logistically complex as the Olympics will have a major disruptive impact on a long list of Olympics constituencies. Athletes’ yearslong training regimens, timed to peak this summer, will have to be replotted, and some may not be able to wait another year.

Broadcasters like Comcast Corp.’s NBCUniversal and Discovery Inc., who together paid more than $1 billion to show the 2020 Games to audiences in the U.S. and abroad, will have their schedules thrown into chaos. Sports organizations that depend on the Olympics to fund their activities every four years will be financially stretched.

NBCUniversal, for example, was counting on the Olympics to promote and help drive subscriptions to Peacock, the company’s direct-to-consumer streaming service that is scheduled to launch nationwide in July.

The Japanese government and the city of Tokyo have invested a total of $7 billion in the Games, including more than $1 billion on a new national stadium. Japanese companies, meanwhile, have provided over $3 billion in sponsorship toward the total Olympic budget of $12.6 billion. While costly, a delay would allow those companies to recoup some of their investment and give the stadium its chance for the spotlight.

The agreement to delay the Games ends a weekslong drama in which the IOC and the Japanese organizers insisted the event would go on even as the coronavirus pandemic gradually shut down much of the world.

The World Health Organization declared the novel coronavirus a pandemic on March 11, and professional sports leagues and American college sports—including the NCAA basketball tournaments and the National Basketball Association—quickly postponed games and suspended operations. Nations closed borders, air travel dropped dramatically and nonessential businesses closed, including gyms and training facilities, as the international death toll from the virus rose.

But even as Olympic-trials events were postponed around the world and the U.S. Olympic and Paralympic Committee closed its training facilities, the IOC maintained it was too soon to make a decision about the Summer Olympics, with the multimillion-dollar centerpiece event still four months away.

On March 17, the IOC issued a statement saying there was “no need for any drastic decisions at this stage; and any speculation at this moment would be counterproductive.” It encouraged athletes to keep training and said it was working with international sports federations to figure out how athletes would qualify in their sports after scheduled trials were postponed or canceled.

Mr. Abe had previously suggested he preferred a delay to cancellation, saying he wanted a full Olympics with spectators and the complete slate of events but at times declining to say whether he believed it had to be held in 2020.

But soon, calls for a postponement began to pile up. One of the first came from a member of the Tokyo organizing committee for the Games, Haruyuki Takahashi, who told The Wall Street Journal on March 10 that a delay of one or two years would be the best option if the coronavirus made it impossible to hold the Games with spectators this year.

As the IOC insisted it remained fully committed to the Tokyo 2020 Games, critics mounted.

On March 20-21, calls to postpone the Games came from USA Swimming and USA Track & Field, whose athletes combined to win more than half of the world-leading U.S. total of 121 medals at the Rio 2016 Olympics. The IOC on Sunday relented and said it would consider a delay.

More pressure mounted, as national Olympic federations, including those of Brazil and Norway, also called for a delay. On Monday night, the USOPC joined the chorus of those calling for the delay.

“How can we consider having an event whose purpose is to bring the world together when the world is sick?” said Greg Meehan, the U.S. swimming women’s national team coach.

The only postponements in Olympic history were for one day at the Munich 1972 Games after terrorists took hostage then killed 11 members of the Israel Olympic team; and some delayed events at Atlanta 1996 the morning after the Centennial Park bombing, according to Olympic historian Bill Mallon.

The 1916, 1940 and 1944 Olympic Games all weren’t held due to world wars. In those years there were fewer than 5,000 participants in the Summer Games, from fewer than 50 countries.

The Tokyo Games were anticipated to be the largest yet, with more than 11,000 athletes from 206 countries expected to compete in 33 sports and 339 medal events.

One of the biggest blows of postponement for Japan will be lost revenue from visitors to the Games. Nomura Securities had estimated the Olympics would bring in around $2 billion in tourism revenue. Many companies had sought to take advantage of the wave of tourists, such as Nintendo, which plans to open a theme park in the summer.

Spectators may also forfeit money spent on tickets. The terms of sale include a force majeure clause absolving the organizers of financial liabilities that covers public health emergencies.

Write to Peter Landers at peter.landers@wsj.com and Rachel Bachman at rachel.bachman@wsj.com

Related slideshow: The Impact of Coronavirus on Sports (provided by imagn)

