About 10,000 residents in China's Hong Kong Special Administrative Region were put under lockdown Saturday in an unprecedented move to contain a worsening COVID-19 outbreak in the city.

The order bans anyone inside multiple housing blocks within the neighborhood of Jordan in Kowloon from leaving their apartments unless they can show a negative test.

Officials said they planned to test everyone inside the designated zone and finish testing within 48 hours before citizens go to work on Monday and "to achieve the goal of zero cases in the district."

For much of last year, Hong Kong kept infections under 10,000 with some 170 deaths by imposing effective social distancing measures. Over the last two months it has been hit by a fourth wave of infections and authorities are struggling to bring the daily numbers down.

Stubborn clusters have emerged in neighborhoods within Yau Tsim Mong, a low-income district with cramped housing. The average flat in Hong Kong is about 46 square meters. It is these kind of buildings where clusters have been located in recent weeks, prompting the city's first lockdown order.

In recent days health officials began carrying out mandatory testing in about 70 buildings in the area but the government has now decided to test everyone in order to "identify those who had infected COVID-19 and cut the chain of transmission," Hong Kong Chief Executive Carrie Lam said on Saturday.

"The action was necessary for public health and would not be carried out only once. I hope citizens can support the government work," Lam said.