LONDON- England's new COVID-19 hotel quarantine system for arrivals from high-risk countries is running smoothly after it was introduced earlier on Monday, the health minister said.

But concerns persist that queuing times at airports could lengthen if there is not sufficient border staff, and there are worries about passengers arriving from high risk countries mixing with travellers from elsewhere while waiting.

Britain has ramped up its border controls to stop new variants of the coronavirus entering the country. Arrivals into England from 33 "red list" countries, including Brazil and South Africa, must now spend 10 days quarantined in a hotel room at a cost of 1,750 pounds.

Hours after the rules kicked in, queues at Heathrow, Britain's biggest airport, were less than one hour long.

"This is working smoothly, we've been working with the airports and with the border force to make sure everybody knows the process," Health Secretary Matt Hancock told Times Radio.

Asked about arrivals mixing, the prime minister's spokesman said: "When people arrive in the UK, the ports and airports have got specific arrangements for those that need to go into quarantine."

All arrivals had to have tested negative for COVID-19 before flying, the spokesman said.

Heathrow Airport, one of five entry points open to people who must quarantine in a hotel, said the stricter measures had successfully come into effect. Airport officials were watching the situation to ensure there were enough border force agents to to avoid unacceptable waiting times and compromising passenger safety, a Heathrow spokeswoman said.

Over the weekend, arrivals at Heathrow, whose passenger numbers were down 90% in January, had faced queues of up to five hours to get through border control. Heathrow said that if queues became too long it would have to stop some flights.

Under the strict measures only British and Irish nationals, or those with residence rights in Britain can travel into Britain from the 33 countries. People can be sent to prison for up to 10 years and face fines of up to 10,000 pounds for breaking the rules. 

More than 4 million people in Britain have tested positive for coronavirus since the pandemic reached its shores, and more than 117,000 have died across England, Scotland, Wales and Northern Ireland - one of the world's highest tolls.

Lockdowns across Britain ban travel for most people, and there are currently about 16,000 to 20,000 people including hauliers arriving each day. That compares to the 350,000-plus daily arrivals by air into UK airports pre-pandemic.

(Reporting by Guy Faulconbridge, Kate Holton, Sarah Young and William James; editing by Angus MacSwan) ((kate.holton@thomsonreuters.com; 0044 207 542 8560; Reuters Messaging: kate.holton.thomsonreuters.com@reuters.net))