Millions more people in the east and south east of England are to enter tier four on Boxing Day, Health Secretary Matt Hancock has announced.
The places moving into the highest level of restrictions – which include a “stay at home” order – border the areas already in tier four.
A number of areas will also move up into tiers three and two.
Mr Hancock also revealed that another new coronavirus variant from South Africa has been detected in the UK.
He said anyone who had been there in the last two weeks must quarantine immediately.
On Wednesday, a further 39,237 people in the UK tested positive for virus – an all-time high – and there were 744 deaths within 28 days of a positive test, according to government figures.
However, cases were thought to be higher in the UK during the spring peak when testing was much more limited.
The health secretary told the Downing Street briefing the old tiering system was not enough to control the new variant of the virus.
Across the country, cases have risen 57% in the last week, he said, and hospital admissions are at their highest level since mid-April.
He said cases had been rising in some of the places close to where the current tier four restrictions are, such as East Anglia, which had seen a “significant number” of the new fast-spreading variant.
“It is therefore necessary to put more of the East and South East of England into tier four.”