Millions more people will come under tougher coronavirus restrictions in the UK from Boxing Day amid concerns over another new strain of COVID-19.

UK Health Secretary Matt Hancock warned the “highly concerning” new variant is believed to be more transmissible than the mutant strain that resulted in the creation of the new Tier 4 restrictions.

It is believed to be behind an increase in cases in South Africa, and has been discovered in two people in the UK thought to be contacts of those who travelled between the two countries in the past few weeks.

From 9am on Christmas Eve, visitors arriving into England who have been in or travelled through South Africa in the previous 10 days will not be permitted entry and direct flights will be banned, the Department for Transport said.

The ban excludes cargo and freight without passengers, and also does not include British and Irish nationals, visa holders and permanent residents, who will be able to enter but are required to self-isolate for 10 days along with their household.

At a Downing Street press briefing on Wednesday afternoon, Mr Hancock said: “This new variant … appears to have mutated further than the new variant discovered in the UK.”

Mr Hancock said the variant coronavirus was spreading at a “dangerous rate” as he announced the measures, which include tough restrictions on mixing with people and the closure of non-essential shops.

Areas moving to Tier 4 from Boxing Day are: Sussex, Oxfordshire, Suffolk, Norfolk and Cambridgeshire, those parts of Essex not yet in Tier 4, Waverley in Surrey and Hampshire – including Portsmouth and Southampton but with the exception of the New Forest.

Tier 4 restrictions include a warning to stay at home, a limit on household mixing to two people outdoors and force the closure of many shops, hairdressers and gyms.

The changes mean 24 million people will now be in Tier 4, or 43 per cent of the population of England.

Health Secretary Matt Hancock during a media briefing on coronavirus in Downing Street, London. Photo: PA

Northern Ireland confirmed a case of the new COVID-19 variant that was first detected in Britain on Wednesday evening.

Meanwhile, tempers flared in Kent as the French reopened the border to allow lorries to cross the Channel for the first time since emergency restrictions were imposed in response to the new variant.

Drivers were being tested for COVID-19 before they are allowed to travel to France.

The Transport Secretary called for “patience” and said work continues to “get traffic rolling”.

China and Brazil have become the latest countries to implement a ban on flights from the UK..

“After much consideration, China has decided to take reference from other countries and suspend flights to and from UK,” Wang Wenbin, a foreign ministry spokesman said on Thursday.

The Brazilian government announced late on Wednesday it was temporarily prohibiting flights that either originated from or passed through the UK in response to the emergence of the Covid variant.

-AAP