The UK «will not hesitate» to add more countries to its travel quarantine list in order to protect public health, the chancellor has said.
Rishi Sunak told Sky News «there is always the risk of disruption» to holidays during the coronavirus pandemic.
It comes amid a surge in cases in France.
Belgium has one of the highest coronavirus case rates in Europe at 49.2 per 100,000 people, compared with 14.3 per 100,000 in the UK.
The Foreign Office is also warning against «all but essential travel» to Belgium, Andorra and the Bahamas.
According to the European Centre for Disease Prevention and Control, France recorded 23.4 cases per 100,000 people in the last two weeks.
France has recorded its highest number of daily coronavirus infections in more than two months, with figures on Wednesday showing 1,695 new cases reported within 24 hours.
For comparison, Spain’s rate was 27.4 per 100,000 around the time it was removed from the UK’s travel corridor list of countries exempt from quarantine restrictions.
Asked whether tourist destinations such as France could be next to be added to the quarantine list, Mr Sunak told the BBC the government was keeping the situation «under constant review» and that people should «be mindful» of the risk of disruption to travel given the global pandemic.
He told holidaymakers they should constantly look at government guidance and «make the best decisions they can, knowing we live in uncertain times».
He told Sky News No 10 was doing «the right thing», keeping the situation «under review on a constant basis» and consulting with scientists and medical advisers. If action was needed, the government would «not hesitate to do that», he said, in order «to protect people’s health».
The new rules for Belgium, the Bahamas and Andorra have already come into force in Wales and will take effect in the rest of the UK from 04:00 BST on Saturday.
Quarantines have already been re-imposed for travellers from Spain and Luxembourg.
But people arriving in England and Wales from Brunei and Malaysia will no longer need to self-isolate, after a decrease in confirmed new coronavirus cases there.
People who do not self-isolate when required to after being abroad can be fined up to £1,000 in England, Wales, and Northern Ireland. Those returning to Scotland could be fined £480, with fines up to £5,000 for persistent offenders.
Last week, Belgium introduced restrictions that meant people could only meet the same five people outside their household in a month.
Joshua Holloway, who works at the University of Ghent, in northwest Belgium, says the «crushing» quarantine news means he will have to abandon plans to visit his family in Shropshire next week.
He says they cannot visit him, because they can’t afford to miss two weeks of work when they return to the UK, adding: «I also cannot go to the UK for an additional period of two weeks prior to when I had planned to travel in order to be able to enjoy a long weekend there.»
Mr Holloway called on No 10 to provide «clearer guidelines» on the number of cases a country would need to hit to trigger its removal from the quarantine exemptions list.
«With the current system, there is no indication at all as to when Belgium will reappear on the quarantine-free list,» he said.