SEOUL — The blurry smartphone videos from Sunday night in China look like something out of a science-fiction movie: Hundreds of workers in an airport parking structure surge against guards in white hazmat suits who block the exit. The workers yell. The security officers yell back through megaphones.

“Just let me go,” shouts one man in the crowd. “I don’t want to die here,” cries out another.

The reason that more than 17,000 employees were sealed inside Shanghai’s main airport on Sunday? Seven cases of the novel coronavirus were linked to the cargo unit.

By Monday morning, Shanghai was back on message, with local officials announcing that 17,719 airport cargo workers had been tested for the virus in one night. All of the 11,544 results received so far came back negative, they said. Official videos showed workers waiting in orderly lines for testing, set to soothing piano music.

Left unanswered was where the workers are now. An airport spokesman declined to say on Monday whether they were still in the airport, taken to quarantine or allowed to go home.

Earlier at a news conference, officials blamed a cargo flight from North America as the possible source of the outbreak, while promising cargo workers access to a vaccine.

“Arrangements will be made for high-risk workers to get a coronavirus vaccine for emergency use, under an informed consent basis,” said Zhou Junlong, vice president of Shanghai Airport Group.

Hundreds of flights into the Shanghai Pudong International Airport on Monday were canceled, according to the flight-tracking app UmeTrip.

China has kept its coronavirus case counts enviably low by cracking down hard on new clusters — harder, perhaps, than any other country. Earlier this fall, the cities of Qingdao and Kashgar each tested millions of residents in a matter of days to guarantee that small clusters had been snuffed out. Photos showed long lines in the streets after dark.

The Shanghai case on Sunday gave a rare glimpse into the human toll of these testing blitzes. Smartphone videos circulating on Chinese social media showed thousands of cargo workers packed into an airport parking facility as they waited their turn for testing. People screamed as they were jostled back and forth.

“Oh, my God, they are fighting,” one woman yelled, as a crowd pushed against the hazmat-suited workers blocking an exit. “They are fighting.”

One person was carried limply away, with someone on video saying the person fainted. The Washington Post was unable to reach airport employees to confirm this.

Shanghai officials decided on action on Sunday when two new positive coronavirus cases were detected, bringing the airport cluster to seven. The new patients were a 49-year-old cargo worker whose colleague tested positive on Friday, and the 31-year-old wife of a cargo worker who tested positive on Saturday, Shanghai’s Municipal Health Commission said.

The overnight testing drive appeared partly an effort by Shanghai officials to show they were doing their utmost to contain the outbreak, after cases continued to pop up at the airport cargo unit weeks after the first one.

On Nov. 8, a 51-year-old cargo worker at the airport — identified by authorities by only his surname, Wang — checked into a hospital with fever, fatigue and a stuffy nose, and he tested positive the next day.

His co-worker, identified as Lan, returned to his home province of Anhui and tested positive there on Nov. 10.

On Friday, a 39-year-old cargo screening handler, named Wu, tested positive, as did his wife and two co-workers. The seventh patient was the wife of one of Wu’s co-workers.

At a news conference Monday, local officials blamed the cluster on a cargo container shipped from North America, saying Wang and Lan had cleaned it together on Oct. 30 before developing symptoms a week later.

“There was a lot of foam cushioning inside, and it was damp,” said Sun Xiaodong, vice director of the city’s pandemic control center. “Research has shown the coronavirus can survive in sealed, damp conditions, and neither of the two was wearing a face mask while cleaning it.”

The officials promised stricter virus prevention measures at the airport cargo unit, but first, the goal was testing everyone within a day — and getting everyone to cooperate.

One video circulating online showed people climbing down a fire escape on Sunday night and trampling across a garden, as they tried to escape the stifling crowds of thousands. Part of the fear appeared to be rooted in the uncertainty over if and when they could leave.

In one of the videos, an announcement blares on a loop: “Please queue for the nucleic acid testing. Don’t push, and be careful of your safety.”

Lyric Li in Beijing contributed to this report.