"We've just found 50 cases of COVID-19 across the city. As the risk of community transmission is high, closed-loop management and massive testing will be carried out."

This situation described by an official with the disease prevention and control center of Hefei, capital of Anhui province, on Sunday afternoon was thankfully only for a drill, during which 12 of the city's nearly 5,000 residential communities were put under lockdown.

The drill was spearheaded by Yu Aihua, Party chief of the city, and lasted for about five hours and involved nearly all of the city's related government departments.

It covered lockdowns in residential buildings, mass nucleic acid testing, epidemiological investigations, the relocation of infected people and close contacts, the supply of necessary materials, as well as the organizing of volunteers.

The drill is just one of the city's efforts to adhere to the dynamic zero-COVID policy. Yu said local officials, who serve the city of 12 million people, should remain vigilant when it comes to the virus.

The city has taken multiple preemptive measures to protect residents from the virus.

On March 29, the city finished building a makeshift hospital with more than 2,000 beds with an investment of 60 million yuan ($9.36 million). The construction of the hospital took only four days.

It's also offering subsidies to truck drivers who transport key industrial and living materials to and from the city, to safeguard supplies for the city and beyond.

Sun Huasong, a community worker from the Nangang township of the city's urban Shushan district, participated in the drill.

Thanks to the drill, Sun said he understood how to respond quickly and professionally to any emergencies.

On Monday, the city reported a 20-month-old boy had tested positive for the virus at Anhui Provincial Children's Hospital in Hefei.

This time, it wasn't a drill.

An epidemiological investigation showed that the boy's grandfather, surnamed Hu, returned from outside the province on April 13 and hid his travel records. He was confirmed as a COVID-19 case later on Monday.

The number of infections in the family rose to five on Monday and two of the family's neighbors were found infected on Tuesday and Wednesday.

As of 7 pm on Tuesday, the city had reported 33 cases in its first COVID-19 outbreak of the year, according to the local health authority.

Sun's job includes helping close contacts to relocate and organizing tests for residents.

"The testing lasted till after 2 am on Tuesday, then I slept in a temporary shelter for a while and got up at around 5 am to deliver living materials to the quarantined households in the community," he said.