People arriving into the UK from Belgium, Andorra and the Bahamas will now need to self-quarantine for 14 days with speculation growing that France may also be added to the list.
The pandemic-related travel restrictions will be imposed from 4 am BST (5 am CET) on Saturday, UK Transport Secretary Grant Shapps said. The new rules have already been in force in Wales since midnight on Thursday.
As well as announcing new quarantine rules, the Foreign Office also advised UK nationals to avoid "all but essential travel" to the three countries.
The countries are the latest to see a change of rules after two-week quarantines were reimposed on people arriving from Spain and Luxembourg at the end of July.
Chancellor Rishi Sunak raised speculation on Friday that more countries, including France, may also be added to the UK's "no-go" list, adding that the UK "will not hesitate" to act.
"What I can say to people is we're in the midst of a global pandemic and that means there is always the risk of disruption to travel plans and people need to bear that in mind," he told Sky News.
"It's the right thing for us to do to keep everything under review on a constant basis, talking with our scientists and medical advisers.
"And if we need to take action as you've seen overnight, we will of course not hesitate to do that and we're doing that to protect people's health," Sunak said.
Travellers arriving from countries on the list who do not self-isolate for the required period risk being fined up to £1,000 (€1,100) in England, Wales and Northern Ireland, and £480 (€530) in Scotland. Repeat offenders could face fines up to £5,000 (€5,500).
The news comes as countries on the continent hard-hit by the new coronavirus grapple with a resurgence in COVID-19 cases.
The rate of infections in Belgium has soared to 49.2 new cases per 100,000 people, according to the latest data collected by the European Centre for Disease Prevention and Control (ECDC).
Infections in France have risen by more than 1,600 cases in a 24-hour period on Wednesday, the highest levels seen in the country since May.
Spain saw a similar rise in infections with a further 1,772 new cases reported on Wednesday.
In Germany, health minister Jens Spahn announced plans on Thursday to carry out coronavirus tests on travellers from arriving from high-risk countries, including the US.