Stricter Covid-19 rules will be imposed across the Lisbon region and Algarve tourism magnet Albufeira as Portuguese authorities try to control a rise in infections that threatens the country's summer holiday season.

"We are in a fight against time between the progression of the disease and the process of vaccination," Reuters quoted Cabinet Minister Mariana Vieira da Silva as saying.

More than half of cases in Lisbon are of the more infectious Delta coronavirus variant, first identified in India.