Officials in New York have introduced quarantine rules for international travellers following the emergence of new Covid-19 variants.
There are fears of new strains in countries including the UK and South Africa.
New York mayor, Bill de Blasio, said all visitors would be ordered to stay for 14-days at the address they provided on arrival.
He added said anyone arriving from the UK would be visited by police to ensure they abide by the rules.
Those who breach them will be fined $1,000 (£737) a day, de Blasio warned.
About 18.4 million coronavirus cases and more than 326,000 deaths have been recorded across the United States, according to Johns Hopkins University.
New York City was at the epicentre of coronavirus outbreak in the country earlier this year, and has again become one of the worst-affected states.
With reports of a new #COVID19 strain in the UK, as of TODAY all international travelers will receive an order to quarantine from @NYCHealthCommr via certified mail. Anyone traveling from the UK will be personally served that order by @NYCSHERIFF.
Learn more: pic.twitter.com/3LgS97jAWR
— Mayor Bill de Blasio (@NYCMayor) December 23, 2020
In a statement, Mayor de Blasio said all inbound international travellers must provide their contact details.
“We are really serious about the fact that if you violate quarantine you are creating a danger for everyone else,” said de Blasio.
“We are in the final battle here; all we have to do is get through these holidays.”
Dozens of countries – including nearly all 27 EU states – have already imposed restrictions on travel from the UK, as governments clamp down on the spread of coronavirus over the Christmas period.
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