Two new cases of novel coronavirus were detected among nucleic test samples taken from 83,413 people in Shenzhen, Guangdong province, officials said at a news conference on Sunday.

The comprehensive tests were immediately carried out to contain the possible contagion since a 41-year-old woman, who sold dairy products at Hema Fresh Supermarket in Shenzhen, was confirmed infected with the COVID-19 on Friday in her hometown of Shanwei, Guangdong.

The incubation period of coronavirus is generally three to seven days. Early detection and isolation are the most effective methods to curb the virus spread," Zhong Nanshan, a prominent infectious disease expert in China, said in a media interview on Sunday.

Thus, massive virus spread was not possible in Guangdong, added Zhong.

The two new cases — a man and a woman—working in the same supermarket were later diagnosed as asymptomatic carriers in Shenzhen, and transferred to a designated hospital under medical observation.

As the supermarket is located in Luohu district, tests are now being conducted on samples from people working and visiting the supermarket after July 24, as well as residents of surrounding neighborhood, said Liu Zhiyong, the governor of the Luohu district government.

First, all employees in the supermarket— 315 persons were tested. Then, 4,208 persons working in the shopping mall where the supermarket is located in were also tested.

All residents, workers and merchants —more than 134,000 in total — near the supermarket are being tested.

Besides, tests are also being carried out for possible contacts. Among the tested people, 5,553 persons are the staff members of the supermarket's 21 chain stores and two warehouses.

Apart from the two persons, all results to date have been negative.

About 287,000 people are on the testing list. "Our testing capacity reached 80,000 samples on Sunday, and we will finish all the tests in three days," said Liu.

About 1,400 medical staff in the city are allocated as sample collectors, working from 8 am to 12 pm.

Meanwhile, Shenzhen inspected and disinfected all chain stores of the supermarket, which were ordered to suspend business and online sales. Related departments had collected 1,426 environment samples and 1,125 food samples in the stores, which were all negative.

"We have traced all sold frozen food from the supermarket. Through the big data, we can find buyers, and then provide door-to-door tests and professional disinfection," said Li Zhong, bureau chief of the municipal market regulation bureau. 

All supermarkets in the city have been required to stop providing eat-in service from Saturday.

Earlier, a sample of frozen chicken wings imported from Brazil tested positive for novel coronavirus nucleic acid. So, every batch of imported frozen food are required to be tested, and their packages should be sterilized. Meanwhile, the government will trace the whole deal process of each product, added Li.

In view of the fact that the pandemic is still raging globally and might rebound in autumn and winter, Shenzhen has promoted abilities of medical treatment, virus testing and epidemiological investigation, said Luo Lexuan, head of the municipal health commission. 

"There are 64 testing organizations in Shenzhen. The testing capacity per day now is more than 120,000 samples. And it can be boosted to 1 million samples a day if necessary," said Luo.

One hospital is treating infected patients while six reserve hospitals are for infectious diseases. If a sudden epidemic outburst, patients could be taken care within 24 hours, added Luo.