LISBON - All COVID-19 cases in the Lisbon area and the popular southern Algarve region are of the more contagious Delta variant, data showed on Tuesday, as Portuguese authorities scramble to bring under control a worrying surge in infections.

Portugal's new daily case numbers have been rising steadily in recent weeks, returning to levels last seen in February when the country was under a strict lockdown battling what was then the world's worst coronavirus surge.

In a report, National Health Institute Ricardo Jorge said the Delta variant first identified in India represented around 86% of cases in Portugal as whole, and 100% of cases in Lisbon and tourist magnet Algarve.

Portugal imposed stricter rules last week to tackle the latest surge in cases, including requiring holidaymakers to show a negative test, vaccination certificate or proof of recovery from COVID-19 to stay in hotels. A night-time curfew is in place in 50 municipalities.

Cases started to gradually increase after Portugal opened to visitors from the EU and Britain in mid-May. But daily deaths remain well below February levels with new cases primarily reported among younger, unvaccinated people who are less likely to fall seriously ill.

The Iberian country of 10 million people has accelerated its vaccination rollout and managed to administer one million doses of the coronavirus jab last week alone.