Happy but cautious at being able to join a mass religious event for the first time since the pandemic began, thousands of Catholic faithful gathered at a sanctuary in Portugal on Friday, as authorities brace for a potential sixth wave of COVID-19.

Retiree Teresa Maria, 62, was one of about 200,000 people who travelled to the famous Fatima Roman Catholic shrine to mark the first of three reported visions of the Virgin Mary, also known as Our Lady, more than 100 years ago.

Last year, only 7,500 were allowed inside the sanctuary and people had to stand in circles to maintain social distancing.

For many, it was a special moment to see the sanctuary finally opening doors to a big crowd after the vast majority of COVID-19 rules were lifted last month. But, as daily infections rise again, Teresa Maria decided to keep her mask on.

"I always try to take precautions," she said as she waited for the farewell procession, one of the highlights of the event, to begin. "We are not free from it because cases are going up."

Portugal has the European Union's highest seven-day rolling average of cases per million inhabitants, according Our World in Data. Health experts believe a "sixth wave is shaping up very intensely".

Deaths and hospitalisations are far below levels suffered during the peak of the pandemic. Those aged over 80 will receive the fourth dose of the COVID-19 vaccine from next week, three months ahead of schedule.

Teresa Maria and others took the opportunity not only to pray for a world without COVID-19 but also for the end of the war that has been ravaging Ukraine since Russia's Feb. 24 invasion.

"So much misery, so much shooting and it doesn't seem like it will end anytime soon," said 79-year-old Arminda Oliveira, shortly after a man with a Ukrainian flag around his neck walked on his knees in prayer close to where she was sitting.

Priests in Fatima blessed a statue of the Virgin Mary and will offer it to a cathedral in the Ukrainian city of Lviv, which has become a refuge and key stop for those fleeing war.

"Even in these difficult times marked by the scourge of war and the virus of the pandemic, rejoice - not in the world but in the Lord," Venezuelan bishop Edgar Parra told the faithful in Fatima.