HONG KONG (BLOOMBERG) - Hong Kong residents returning from Britain must stay at a government-run quarantine centre, though the city slashed the number of days arrivals must spend there.

Britain will be added to a category that calls for the strictest measures in which travellers are sent to Penny's Bay Quarantine Centre, according to a government statement. The change takes effect on Tuesday (Dec 21).

People coming from nations on the list will now spend four days at the facility - down from the previous seven - if they have a reservation at a designated hotel for the rest of their 21-day quarantine.

The government also said it would suspend flights if four or more passengers from any route are found to be infected with Covid-19 upon arrival in Hong Kong within a seven-day period. Each suspension will last for two weeks.

It banned Cathay Pacific's flights from New York to Hong Kong through Jan 2 after three passengers on one plane were found to be infected.

The previous rules, where flights are suspended if five or more passengers from any one place test positive on arrival within a week or 10 or more passengers develop Covid-19 after arrival, remain in place.

The moves highlight Hong Kong's strict approach to dealing with the virus, one that is coming under mounting criticism. The local government is keen to align itself with China's strict Covid-zero policies in hopes of reopening their border.

The decision comes as the British government considers imposing a Christmas lockdown to stop a surge in the number of Covid-19 cases. Prime Minister Boris Johnson's scientific advisers recommended bringing in tougher rules "very soon" to keep hospitalisations from escalating to thousands a day.

Britain joins the United States, along with some African countries, in facing the tough measures. The US was added to the category earlier this month.