From midday Friday (26 November), South Africa, Botswana, Lesotho, Eswatini, Zimbabwe and Namibia will be added to the list.
Non-UK and Irish residents who have been in these countries in the previous 10 days will be refused entry into England.
Passengers arriving from 4am Sunday (28 November) in England will be required to book and pay for a government-approved hotel quarantine facility for 10 days.
British nationals arriving from these six countries between midday Friday (26 November) and 4am Sunday (28 November), and who have been in these countries within the last 10 days, must quarantine at home for 10 days and take PCR tests on Day 2 and Day 8, even if they already have a lateral flow test booking, the department of health confirmed.
The Scottish government has implemented the same restrictions and the Foreign Office is now advising against all but essential travel to South Africa.
The move comes as Variant B.1.1.529 is declared a "Variant under Investigation (VuI)" by the UK Health Security Agency (UKHSA). No cases have yet been identified in the UK.
A temporary ban on commercial and private planes travelling from the six countries will also come into force at midday on Friday (26 November) until 4am Sunday (28 November).
Transport secretary Grant Shapps said: "We’ve always maintained public safety is our number one priority, which is why we’ve kept in place measures which allow us to protect the UK from new variants.
"We’re taking this early precautionary action now to protect the progress made across the country, and will continue to keep a close eye on the situation as we continue into the winter."
British nationals in these countries have been advised to check FCDO travel advice and follow local guidance.
