HONG KONG >> Thousands of Hong Kong residents were locked down Saturday in an unprecedented move to contain a worsening outbreak in the city, authorities said.

Hong Kong has been grappling to contain a fresh wave of the coronavirus since November. Over 4,300 cases have been recorded in the last two months, making up nearly 40% of the city’s total.

Coronavirus cases in Hong Kong’s Yau Tsim Mong district — a working-class neighborhood with old buildings and subdivided flats — made up about half of the infections in the past week.

Sewage testing in the area picked up more concentrated traces of the COVID-19 virus, prompting concerns that poorly built plumbing systems and a lack of ventilation in subdivided units may present a possible path for the virus to spread.

Authorities said in a statement Saturday that an area comprising 16 buildings in Yau Tsim Mong will be locked down until all residents have undergone tests. Residents will not be allowed to leave their homes until they have received their test results to prevent cross-infection.

“Persons subject to compulsory testing are required to stay in their premises until all such persons identified in the area have undergone testing and the test results are mostly ascertained,” the government said in a statement.

Hong Kong has previously avoided lockdowns in the city during the pandemic, with leader Carrie Lam stating in July last year that authorities will avoid taking such “extreme measures” unless it had no other choice.

The restrictions, which were announced at 4 a.m. in Hong Kong, are expected to end within 48 hours, the government said.

It appealed to employers to exercise discretion and avoid docking the salary of employees who have been affected by the restrictions and may not be able to go to work.

Hong Kong has seen a total of 9,929 infections in the city, with 168 deaths recorded as of Friday.