Hong Kong extended mandatory quarantine to three weeks for all international inbound travellers.
The tighter restrictions apply to arrivals except from mainland China, Macau and Taiwan.
It took the measures to try to contain the spread of the new strain of Covid-19 which is thought to be significantly more infectious.
Officials say expert advice suggests the incubation period for the new variant in some people may be longer than 14 days.
All inbound passengers will now have to undergo compulsory quarantine in designated hotels for 21 days.
It imposed a ban on travellers who have been in South Africa in the last 21 days and banned flights from the UK last week.
Health officials said two Hong Kong residents who returned recently from the UK may jave been infected with the new strain.
Written by Ray Montgomery, Asia Editor
