Travellers arriving in England from Slovenia and Guadeloupe after 4am on Saturday will have to isolate for two weeks.
The two countries are being added to the quarantine list, Transport Secretary Grant Shapps announced.
But Thailand and Singapore are being removed from the list.
Mr Shapps tweeted: "A reminder that travellers to the UK (from ANY location) MUST complete a passenger locator form by law.
"This is vital in protecting public health and ensuring those who need to are complying with self-isolation rules."
In Slovenia, the COVID-19 case rate per 100,000 people has risen from 14.4 to 29.1 in the week ending 16 September.
And the government said that in Guadeloupe there has been a 558% spike in the same metric over the past three weeks.
The Department for Transport vowed to "take decisive action if necessary to contain the virus, including removing countries from the travel corridors list rapidly if the public health risk of people returning from a particular country without self-isolating becomes too high".
Ministers say countries where the coronavirus infection rate is higher than 20 per 100,000 people are at risk of being added to the list - but last week the UK tipped over that threshold itself.
Since then, tough restrictions have been imposed on millions of people.
The latest will come into force on Friday in Northumberland, North Tyneside, South Tyneside, Newcastle-upon-Tyne, Gateshead, Sunderland and County Durham.