No earthquake had been reported in the region, which was only experiencing light winds.
The swaying of the 21-year-old building started at approximately 12:31 p.m. local time on May 18.
Videos circulating on social media showed people running away from the building, with some screaming, holding umbrellas, and looking back over their shoulders.
Chinese media reported that all 15,000 evacuees escaped from the building within 90 minutes. Nobody was injured.
On May 19, local media reports said the building had started to sway again, although not as dramatically as it had on May 18. The building remained closed for investigation, although the property manager—Shenzhen SEG Co. Ltd.—had allowed shop owners from the major electronics market into the first 10 levels of the building to collect their goods.
Three floors of crypto-mining computers in the electronics market—one of the main crypto-mining markets in China—weren’t accessible due to the incident.
Late May 19, the local government announced that investigating engineers had been unable to determine the cause of the swaying, while noting that none of the building’s movements since they started monitoring late May 18 had exceeded building code limits for skyscrapers.
Experts found “no safety abnormalities in the main structure and surrounding environment of the building,” the local government said in a statement.
Local media reports on May 20 following preliminary assessments noted that the skyscraper didn’t have a tuned mass damper—a large pendulum-like device installed in high-rises to reduce excessive swaying.
The department of emergency management of Guangdong Province also confirmed that the preliminary findings pointed to vertical rather than horizontal movement, which was said to be caused by factors such as winds, underground rail lines, and the expansion of steel with rising temperatures.
On May 19, SEG’s stock price had dropped more than 7 percent on the Shenzhen Stock Exchange, and closed 4.88 percent lower than the opening price.
SEG Plaza is a landmark in Shenzhen. The building is 1,167 feet (355.8 meters) high, and the architectural height is 957 feet (291.6 meters).
The building has 75 floors above ground and four floors underground. The underground floors are parking and equipment levels. The first 10 floors above ground are the electronic market, and the upper floors are offices and a hotel, according to Shenzhen city government-run Shenzhen News.
According to the online database Council on Tall Buildings and Urban Habitat, SEG Plaza is the 18th-tallest building in Shenzhen and the 104th tallest in China.
Building collapses have been reported in China. On March 7, 2020, 29 people were killed as the five-story Xinjia Hotel, which was being used for COVID-19 quarantine, collapsed in Quanzhou in southern China’s Fujian Province.