Thousands of people, many disabled or ailing, have been evacuated on Sunday from the shrine at Lourdes in southern France after a bomb threat on the Catholic holy day of Assumption.

The pilgrims returned after explosives experts scoured the area.

Some 30,000 pilgrims were at the site, whose spring water is reputed to have healing powers, when Lourdes police received a threat late in the morning saying a bomb would hit the site on Sunday afternoon.

In an announcement read in six languages, authorities ordered everyone evacuated just as a midday Mass was supposed to begin.

About 900 gravely ill pilgrims, including many on stretchers, were taken to a secure place while explosives experts with sniffer dogs fanned out around the shrine, Lourdes Mayor Jean-Pierre Artiganave said on France-Info radio.

While the site was off-limits to pilgrims, a scheduled prayer service was held anyway, in the shadow of the spring and a statue of the Virgin Mary. After about five hours, the shrine reopened and Assumption ceremonies resumed, said another shrine spokesman, David Torchala.

No information was available about the source of the threat.