The Hong Kong government locked down thousands of people yesterday so they could undergo the first forced mass testing exercise since the onset of the Covid-19 pandemic.

More than 3,000 government staff were deployed in a densely populated inner city area on the Kowloon peninsula. It was a multi-bureau effort that involved setting up 51 testing stations and going door to door to get people to go for the tests in a specified, restricted area in the neighbourhood of Jordan.

The government said it aims to wrap up the whole exercise in 48 hours so as to "achieve the goal of zero cases in the district" and allow residents to get to work by 6am tomorrow.

Everyone in the cordoned area are to stay in their premises after the tests, while anyone who visited the area for more than two hours in the past two weeks must also go for testing.

Speaking to reporters yesterday afternoon after an inspection, Chief Executive Carrie Lam asked the public for their understanding for any inconvenience or confusion caused, given the necessity of the exercise.

Arrangements for a place to rest, she said, were made for people who did not live in the area but were affected by the lockdown.

While it is the first time the government has resorted to a lockdown, Mrs Lam stressed that it is not the same as lockdowns in other countries.

"I must make it very clear that what we are doing is not what people see in other places as a lockdown, because a lockdown normally means that you are not allowed to go out for a period.

"But in our case, this prohibition is linked to the tests... Once the compulsory testing for the entire area has been completed, then the order will be lifted and people will be allowed to go out," she said, when asked if she adopted such an approach after pressure from Beijing.

From Jan 1 to 20, the specified Jordan area recorded 162 confirmed cases involving 56 buildings.

The government said a higher ratio of sewage samples found in buildings in the restricted area in the past few days had tested positive, compared with samples from other areas of Jordan, implying that possibly infected persons could be present at those places.

It added that the buildings in the restricted area are old, lack maintenance, and subdivided units are common, so infection risks are high.

"After risk assessment, we think it is necessary to issue a restriction-testing declaration for the restricted area to break the transmission chain in the district and dispel the worries of residents in the district," the statement added.

The government appealed to employers to be understanding, adding that it hopes the "temporary inconvenience will completely cut the local transmission chains".

As at 1pm yesterday, at least 3,000 people in the area had been tested. Working staff had visited over 50 buildings, involving around 1,000 households.

"There's a chance some people are in the incubation period, so we will not rule out conducting a second round of testing. We will consider this. Because of the incubation (period), some people in this area may already have been tested but we will require everyone in this area to undergo tests anyway," Secretary for Health Sophia Chan said.

Only those with confirmed negative results can leave the area while those found positive will be sent for treatment, she added.

Overnight on Friday, workers started loading food and cleaning supplies to the area as officials cordoned off the restricted zone to set up temporary specimen collection stations.

Some residents were spotted "fleeing" late into the night with their luggage and pets, local media reported. This came after news was leaked earlier in the day about the pending lockdown, but health officials did not comment on it when asked at the daily briefing.

Confusion was obvious as media reported there were residents who wanted to retrieve their goods and pets from the restricted area but were left stranded, saying they were not informed of the lockdown.

Yesterday, Hong Kong recorded 81 new Covid-19 cases, of which 78 were local, 35 were untraceable and 21 were from Yau Tsim Mong, while six were from Sham Shui Po.

It has been a year since the city recorded its first confirmed Covid-19 case - a 39-year-old man from Wuhan who landed in Hong Kong on Jan 22 via the high-speed rail. The tally has now risen to 10,009 cases and 168 deaths.