A huge thunderstorm in Madrid Saturday night forced Pope Benedict to cut short his speech to an estimated one million young pilgrims gathered for the church's world youth festival.

The freak storm gave the outdoor prayer vigil at a Madrid airfield a dramatic climax. Firefighters checked the stage before allowing the leader of the world's 1.6 billion Catholics to return. He thanked the gatherers for their “joy and endurance,” adding that their strength was “greater than the rain.”

Earlier in the day, firefighters had sprayed the crowds with water from hoses in a bid to stave off the near 40-degree Celsius heat. The pilgrims also sought shade from umbrellas, trees, tarps and tents.

Before his speech, Pope Benedict had been greeted by Spain's crown Prince Felipe and Princess Letizia.

This was the pontiff's third World Youth Day. It's a once-every-three-year gathering of young Catholics from around the world that was launched a quarter century ago by Pope John Paul II in a bid to reinvigorate and spread the faith among the young.

Observers say it has the feel of a week-long rock concert and camping trip, with bands of flag-toting pilgrims roaming through Madrid's otherwise empty streets to take part in prayer and education sessions,

Masses, cultural outings and papal events.

As he awaited the vigil, a 16-year-old student from Tanzania said he was not able to understand the pope's exact words in Spanish, but it was an amazing experience to share the moments with so many people from so many different countries.