EasyJet will fly larger planes and lay on extra flights to bring UK holidaymakers back from Portugal before quarantine rules come into force on Tuesday.
More than 1,000 additional seats have been added on routes from Faro to Gatwick, Luton, Manchester and Bristol.
EasyJet chief executive Johan Lundgren said: "We know first-hand from our customers what a blow this sudden decision to put Portugal on the amber list is.
"With many British tourists currently in Portugal our priority is to help the customers who need to return ahead of the Tuesday deadline.
"We are providing over 1,000 additional seats from Portugal to the UK by flying larger aircraft on flights and adding some additional flights where there is demand.
"And, for customers who need support with testing requirements, we're working with approved testing partner Collinson to provide support to customers in Portugal who need to arrange new tests."
The scramble to get home comes after Transport Secretary Grant Shapps announced that Portugal would be reclassified amber from green.
The change means that returning Brits will have to quarantine at home for ten days and pay for costly tests.
This morning a Portuguese epidemiologist claimed the decision to move Portugal to the amber tier was "an overreaction".
Professor Henrique Barros, president of Portugal's National Health Council, said the country's overall coronavirus situation is "relatively stable".
He made the comments after Communities Secretary Robert Jenrick said positive cases had doubled in the last three weeks in Portugal.
Prof Barros told Sky News: "We didn't reach such an increase, except as I said in a specific area around Lisbon.
"The overall picture in the country, we didn't reach such figures."
The decision to move Portugal to the amber list means people returning to the UK from there must self-isolate at home for 10 days.
"I think it's an overreaction," Prof Barros said.
The health chief explained that the rise in infections are mainly among people aged under 40, and there is a "very low incidence of cases" in the over-50s.
He stressed that hospital admissions at the present time are "very low", at less than 25 people per million.
Officials in the country "pay a lot of attention" to monitoring the virus, he added.
Mr Jenrick acknowledged that the situation was "frustrating" for travellers, but insisted the Government was "clear" that the classification of green list countries could change.
