The order effective on Saturday covers multiple housing blocks in the neighbourhood of Jordan in Kowloon Peninsula.
Thousands of Hong Kong residents are locked down for the first time, 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 per cent of the city's total.
Coronavirus cases in Hong Kong's Yau Tsim Mong District, a working-class neighbourhood with old buildings and subdivided flats, represent about half of the infections in the past week.