Thousands of Catholics made a pilgrimage to the French shrine of Lourdes today to mark the Feast of the Assumption amid tight security following the murder last month of a priest in Normandy.

Groups from across Europe, the Middle East and Asia gathered in the sanctuary in the foothills of the Pyrenees in south-west France celebrating the ascent into Heaven of the Virgin Mary, in the first major Catholic event in France since Jacques Hamel was killed by two men supporting Islamic State.

"We've come to pray for peace in the world, which seems to be in chaos," Piet Tarappa, an Indonesian businessman who came from Jakarta with 35 other pilgrims and a bishop, told the news agency AFP.

Lionel Ambroise, a 29-year-old French engineer living in Brussels, told AFP that he had come to "reflect on the world and France in particular, which is going through a crisis."

There was a heavy presence of armed security for the ceremony, which culminated with an open-air Mass at the spot where Mary is said to have appeared to a shepherd girl in 1858.

AFP reported that soldiers in fatigues with automatic rifles were guarding the pilgrims as a helicopter flew overhead. Some 500 security personnel were deployed to protect the crowd of up to 25,000 worshippers expected at the Mass.

On arrival, pilgrims had their bags searched on entry to the site, where bomb disposal experts with sniffer dogs were on standby.

Following the truck massacre in Nice on 14 July, the streets around the sanctuary were sealed off to traffic.

The French Cardinal Philippe Barbarin dedicated his homily to his country, which had been "rocked by so much suffering since January 2015 [when the satirical magazine Charlie Hebdo and a Jewish grocery were attacked] and which was again cruelly hit last month."

Barbarin said his message was addressed to "all the faithful", including Muslims and Jews.

"It's important to show that life goes on," one of the pilgrimage coordinators, Matthieu Guignard, told AFP. "It's not because a few fanatics try to sow fear that we should abandon our faith, our beliefs, our way of living."

Around six million people per year come to Lourdes, making it one of the biggest sites of Catholic pilgrimage in the world.

Sick and disabled people especially flock to the shrine and bathe in a spring in the cave where Saint Bernadette said she saw Mary, believing the water to have healing properties.