The “exceptional” measure has been implemented “to prevent possible threats to public order and internal security”, which will last until August 7, according to a government decision.

The identity checks at the borders will be “random and not systematic”, Portugal’s interior minister Jose Luis Carneiro said yesterday, adding there will be coordination with Spanish, French, and Italian authorities.

Portugal is expecting about a million pilgrims from around the world, according to organisers, to attend the gathering of young Catholics from August 1 to 6.

Originally scheduled for August 2022, the event was postponed because of the Covid-19 pandemic.

Francis, 86, has been recovering from surgery since early June but has confirmed his attendance.

The five-day visit by the head of the Catholic church will be marked by a full agenda with around 20 meetings and 11 speeches.