Pre-departure tests will be required for all people arriving in the UK, as Sajid Javid announced Nigeria would be added to the travel Red List.
The Health Secretary also confirmed there were now around 160 cases of the Omicron variant around the UK - with 130 in England.
The pre-departure tests - to be taken a maximum of 48 hours before departure time - will be required from 4am on Tuesday, and will apply to all travellers arriving in the UK.
At the same time, Nigeria will be added to the travel red list, meaning that from 4am on Monday only UK citizens or residents can enter the UK from Nigeria, and those that do must quarantine in a hotel.
The move was made after Mr Javid said 27 cases of Omicron in England were linked to recent travel from Nigeria.
Earlier, Dr Jenny Harries, UKHSA chief executive, said: "Increased case detection through focused contact tracing has led to more cases of the Omicron variant being identified and confirmed, as we have seen in other countries globally.
Mr Javid said: "We've kept the data under review since last week when we learned about Omicron, and we're seeing an increasing number of cases linked to travel.
"And again, we've always said we'd act swiftly if we need to, if the changing data requires that. And that's why we've decided to bring in this change on pre-departure tests."
Mr Javid stressed the measures would be temporary, and would be removed "as soon as we possibly can."
Asked why the Government had waited so long to introduce the new measures, he said it was "important to have a balanced approach."
He said: "The measures that we introduced this time last week which were around the day two PCR tests when everyone arrives back in the UK and everyone self-isolating until you get a negative result, and some of the other measures around red listing, I think have been the right response.
"But when the situation changes, if it requires more action, it's absolutely right the government acts swiftly."
Mr Javid confirmed British travellers already in Nigeria would have to put in place measures through the managed quarantine system, and pointed them to the Government's website for further information.
But Mr Javid said that people should "carry on" with Christmas plans, and enjoy the holiday season "as usual."
Following the addition of Nigeria, the UK red list in full is:
- Angola
- Botswana
- Eswatini
- Lesotho
- Malawi
- Mozambique
- Namibia
- Nigeria
- South Africa
- Zambia
- Zimbabwe
