After China largely brought the virus under control, hundreds have been infected in Beijing and cases have emerged in neighboring Hebei province.
Health officials said Sunday that Anxin County -- about 150 kilometers from Beijing -- will be "fully enclosed and controlled", the same strict measures imposed at the height of the pandemic in the city of Wuhan earlier this year.
Now, only one person from each family will be allowed to go out once a day to purchase necessities such as food and medicine, the county's epidemic prevention task force said in a statement, AFP reported.
Earlier the county had been subject to some travel restrictions, but now individuals are only allowed to leave their homes to seek medical treatment, the notice said.
The move comes after another 14 cases of the virus were reported in the past 24 hours in Beijing, taking the total to 311 since mid-June.
The outbreak was first detected in Beijing's sprawling Xinfadi wholesale food market, which supplies much of the city's fresh produce and sparked concerns over the safety of the food supply chain.
Businesses in Anxin County had supplied freshwater fish to the market, state news agency Xinhua reported.
Some 12 cases of the novel coronavirus were found in the area, including 11 linked to Xinfadi market, the state-run Global Times reported.
The new cases in Beijing have prompted fears of a resurgence of the virus in China.
The capital has mass-tested wholesale market workers, restaurant workers, residents of medium and high-risk neighborhoods and delivery couriers over the past week.
Testing has now expanded to include all employees of the city's beauty parlors and hair salons, the Global Times said.
Beijing city official Xu Hejian told reporters Saturday: "There is no room for us to relax."
City officials have urged people not to leave the city, closed schools again and locked down dozens of residential compounds to stamp out the virus.
But Wu Zunyou, chief epidemiology expert at the Chinese Center for Disease Control and Prevention, told reporters last week the new outbreak had been "brought under control", and officials lifted a weeks-long lockdown imposed on seven communities in Beijing Friday.