China tells Winter Olympic spectators to clap, not cheer, for athletes, and Xi’an, a major city, locks down.

ZHANGJIAKOU, China — Spectators at the Winter Olympics next February should clap but not shout in support of athletes. Waiters, cleaners and other support staff will not be allowed to leave Olympic venues to visit their families. And any Olympic participants leaving the vicinity for the rest of China will be required to spend at least one week in quarantine, followed by at least two weeks of isolation at home.

As the Omicron variant spreads rapidly around the globe, China is taking elaborate precautions to prevent the coronavirus from reaching its own population or participants in the Winter Games. Chinese officials are also bracing the public for the inevitability that some infections will emerge at the Olympics, where everyone will face daily P.C.R. tests.

“A certain number of positive cases will become a high probability event,” Han Zirong, the secretary general of Beijing’s Winter Games organizing committee, told reporters on Thursday.

China has barred overseas spectators from entering the country. It is allowing vaccinated foreign athletes, trainers, coaches, referees, journalists and a few others to enter without enduring the usual two or more weeks of quarantine followed by a week of home confinement.

The exemption, however, comes with a stringent requirement that foreigners not leave a “closed loop” of hotels and sports venues, linked by special buses and trains.

“We must never go outside the closed loop, let alone reach the city level — this is our bottom line,” said Huang Chun, deputy director of the Olympic organizing committee’s Office of Epidemic Prevention and Control.

China has reported dozens of coronavirus cases daily this week. On Thursday, the local authorities locked down Xi’an, a city of 13 million people. At least 242 cases have occurred there in an outbreak this month. Beijing has not divulged how many involve the Omicron variant.

The country has been mostly successful in controlling the virus by quarantining hundreds of close contacts of infected people, and in some cases contacts of contacts. But similarly broad measures at the Olympics could make it hard to hold the Games.

Some precautions are already visible at a ski resort in the mountains near Zhangjiakou, about 100 miles northwest of Beijing, where nearly half of the Olympic events will be held. Thick, clear plastic sheeting from floor to ceiling separates bus drivers from their passengers.

At the resort’s high-speed-rail station, visitors must provide proof of a negative P.C.R. test in the preceding 48 hours. Also required is proof on a smartphone app that the traveler has not visited any Chinese city in the previous two weeks that has had a recent infection.

For construction workers putting the finishing touches on the venues, the authorities already do nucleic acid tests once every three days, Jia Maoting, the general manager of the Olympic Sports Construction and Development Company, told reporters during a visit to the Olympic ski jump venue.

Mr. Han, the secretary general of the Olympic organizing committee, cautioned that further measures may be added in the weeks to come. “Everything depends on the changes in the global and Chinese epidemic situation,” he said, “especially the infectiousness of the new mutant strain, Omicron.”

Liu Yi and Li You contributed research.