UK visitors to Portugal who are not fully-vaccinated against Covid-19 must quarantine for two weeks on arrival.
The strict new rules came into force today (Monday) and state anyone travelling to mainland Portugal by air, land or sea, will have to prove they have been given two doses the vaccine at least two weeks previously, or self-isolate "at home or a place indicated by health authorities".
The regulations will be in place until July 11 at the earliest and apply to mainland resorts. The Portuguese island of Madeira is not covered by the restrictions.
Most new cases of Covid are concentrated in the area around capital Lisbon, the southern Algarve, a favourite with UK holidaymakers, has the highest "R" number of 1.34, local health reports state.
On Thursday, Portugal imposed stricter rules, including forcing restaurants to shut earlier over the weekend in Lisbon and in the Algarve resort of Albufeira.
"We are in a fight against time between the progression of the disease and the process of vaccination," Cabinet Minister Mariana Vieira da Silva said.
Portugal is currently on the UK government's amber travel list, which means passengers also have to isolate for 10 days when they arrive back in Britain.
It was taken off the green list, which doesn't require passengers to quarantine, last month over concerns about a rise in cases.
Germany is also trying to get the European Union to ban all travellers from the UK - regardless of whether they have had a coronavirus vaccine or not. However the plan is meeting resistance from Spain and Greece.
