London, most of Essex and parts of Hertfordshire will move into England’s highest tier of Covid restrictions, Health Secretary Matt Hancock has said.
The areas join tier three at 00:01 GMT on Wednesday, meaning some 34 million people will face the toughest rules.
A new variant of coronavirus has been identified that "may be associated" with the faster spread in southern England, Mr Hancock added.
Pubs and restaurants in tier three must close except for takeaway and delivery.
Also under the rules, sports fans cannot attend events in stadiums, and indoor entertainment venues - such as theatres, bowling alleys and cinemas - must remain shut.