UK-bound arrivals from South America and Portugal will be banned from Friday over concerns about the Brazilian coronavirus variant.
Transport Secretary Grant Shapps said the change would come into force from 04:00 GMT.
British and Irish citizens and foreign nationals with residence rights will still be able to travel but must isolate for 10 days, he said.
The decision was announced following a meeting of ministers on Thursday.
The ban applies to people who have travelled from, or through, Argentina, Brazil, Bolivia, Cape Verde, Chile, Colombia, Ecuador, French Guiana, Guyana, Panama, Paraguay, Peru, Suriname, Uruguay and Venezuela in the last 10 days.
Mr Shapps said Portugal had been included “given its strong travel links with Brazil” – but there would be an exemption for hauliers travelling from the country to allow the transportation of essential goods.
He said suspending travel from that European country would act “as another way to reduce the risk of importing infections”.
On Wednesday, Prime Minister Boris Johnson said he was “very concerned” about the Brazilian variant of the virus.
New variants of Covid-19 have previously been identified in the UK and South Africa, with many countries imposing restrictions on arrivals from both nations.
Several Central and South American nations had already restricted travel from the UK, including Chile, El Salvador, Guatemala and Panama, while others such as Argentina and Uruguay have closed their borders to non-resident foreign nationals.
The Department for Transport said under the ban any exemptions would not apply, including those for employment, and people who live with someone who has travelled from one of the banned countries will have to self-isolate for 10 days.
The travel ban comes after it was announced a requirement for arrivals into England to test negative for coronavirus 72 hours before their journey will now come into force at 04:00 GMT on Monday.
Scotland is taking the same approach to international travellers but will implement the policy on Friday, while Wales and Northern Ireland are expected to announce their own plans in the coming days.
Mr Shapps said the new rules had been delayed from Friday “to give international arrivals time to prepare” but Labour leader Sir Keir Starmer said people would be “bewildered” by the delay and would “feel that we’re exposed”.