TOKYO—The Olympics opening ceremony began Friday stripped of pomp after the pandemic forced a change to the bustling celebrations that opened previous Games.

A simple stage featuring a model of Mt. Fuji was set up as the focus of a show seen by fewer than 1,000 people at the National Stadium in Tokyo. Performances will highlight the challenges of the pandemic for athletes and remember those lost to Covid-19. 

Planners are hoping to hold the attention of the global television audience with celebrations of Japanese culture, including the use of a medley of videogame songs during the “parade of nations” featuring athletes from more than 200 countries.  Only around 5,700 athletes will join the parade, down from more than 10,000 in the opening ceremony in Rio in 2016. The U.S. group is set to be around 260, less than half of the 613 athletes in Team USA. “It will be a very, very sober ceremony, meaning very little cast and no mass choreography because Covid can’t allow it,” said Marco Balich, a senior adviser to the executive producer of the ceremony, ahead of the start.

The Covid-19 pandemic hangs over everything Olympic-related, with the opening ceremony happening after a year’s delay. Athletes such as U.S. tennis star Coco Gauff have had to withdraw because of infection.

Among those watching are first lady Jill Biden and Japan’s Emperor Naruhito, who will declare the opening of the Games, though he is expected to avoid the word “celebrate” in deference to the pandemic.

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The lack of people in the stands was likely to be jarring for the athletes as they marched into the stadium grouped by country.

“Normally, the thrill is seeing all the people in the stadium when you enter, and waving to friends and family,” said Matt Suggs, chief executive of USA Shooting.

Athletes were free to join, but under Covid-19 restrictions they were told not to arrive in the Olympic Village sooner than five days before the start of their competition. That means those who are competing later during the Olympics may not be in Japan for the ceremony.

The International Olympic Committee said that while all countries would be allowed one male and one female flag bearer for the parade, some wouldn’t have two flag bearers because of restrictions on periods of stay in Japan and travel complexities. 

Most coaches and officials were asked not to take part in the parade. Athletes typically mingle together in the center of the stadium during Olympic opening ceremonies, but they were told to keep to social distancing guidelines this time and wear masks.

The ceremony was briefly thrown into crisis on Thursday when the director of performances was fired because of a joke he made in the 1990s about the Holocaust. The organizers of the Games later confirmed the ceremony would go ahead without any changes.Mr. Balich, who was the executive producer for the opening ceremony in Rio, said the organizers decided the appropriate artistic feel of the Tokyo ceremony would be Japanese minimalism. 

“There are no smoke and mirrors, no super special effects,” he said.

The climax of the show will be the lighting of the Olympic cauldron to signal the formal start of the Games. The organizers are keeping the identity of the person who will light the cauldron secret until the last minute. 

Write to Alastair Gale at alastair.gale@wsj.com