Portugal, which has one of the world's highest rates of vaccination against COVID-19, says it will reimpose some restrictions to stop a surge in cases, ordering all passengers flying into the country to show a negative test certificate on arrival.
"It doesn't matter how successful the vaccination was, we must be aware we are entering a phase of greater risk," Prime Minister Antonio Costa told a news conference on Thursday.
"We have seen significant growth (in cases) in the EU and Portugal is not an island," he added.
Portugal reported 3773 new cases on Wednesday, the highest daily figure in four months, before dropping to 3150 on Thursday.
Deaths, however, remain far below levels registered in January when the country faced its toughest battle against COVID-19.
About 87 per cent of Portugal's population of just over 10 million is fully inoculated against the coronavirus and the country's speedy vaccination rollout has been widely praised.
That has allowed it to lift most of its pandemic restrictions.
But, as another wave of the pandemic sweeps across Europe, the government reintroduced some old rules and announced new ones to limit the spread in the run-up to the holiday season.
The measures come into force on December 1.
Speaking about the new travel rule, Costa said airlines would be fined 20,000 euros ($A31,187) per passenger if they transport anyone who does not carry proof of a COVID-19 test, including for those who are fully vaccinated.
Costa has also announced that those fully vaccinated must also present proof of a negative coronavirus test to enter nightclubs, bars, large events and care homes, and that the EU digital certificate would be required to stay in hotels, go to the gym, or dine indoors in restaurants.
Remote work will be mandatory during the first week of January to control the spread of the virus after the holiday festivities.
Australian Associated Press