TORONTO -- Pope John Paul II called on young Catholics to turn away from the secularism that characterized the 20th century and turn back to god at a vigil for hundreds of thousands pilgrims Saturday.

Invoking the specter of the September 11 terror attacks and criticizing the godlessness of the last century, the Pope encouraged the young faithful to use their faith to build a better world, AFP reported.

"A new generation of builders is needed, moved not by fear or violence but by the urgency of genuine love. They must learn to build, brick by brick, the city of God within the city of man.

"You must be those builders! You are the men and women of tomorrow," he said.

"The future is in your hearts and in your hands. God is entrusting to you the task, at once difficult and uplifting, of working with him in the building of the civilization of love."

Seated on an 40,000 square foot (3,700 square meter) stage, below an illuminated cross, the 82-year-old pontiff addressed a crowd of up to 550,000 Catholics, at his second public appearance at World Youth Day events.

Spread out over a huge field, the young pilgrims -- most of whom will camp out overnight in advance of a papal mass early Sunday -- held candles as the vigil continued late into the night.

Camped out on sleeping bags and under makeshift tents at Downsview park, a former military base, they listened as the Pope talked about the questions raised by the terror attacks.

Calling the attacks on New York and Washington, "an icon of a world in which hostility and hatred seem to prevail," he said it raised the question "on what foundations must we build the new historical era that is emerging from the great transformations of the twentieth century? "Is it enough to rely on the technological revolution now taking place, which seems to respond only to criteria of productivity and efficiency, without reference to the individual's spiritual dimension or to any universally shared ethical values?" The six days of youth celebrations -- mass, prayer, confession and religious instruction -- wound up Sunday with an open-air papal mass.

Pope John Paul II encouraged young Catholics to be the builders of peace and freedom and to reject modern world's secular direction, at a vigil here late Saturday.

In a strong, clear voice and speaking in several languages, the 82-year-old pontiff told an estimated 500,000 pilgrims at Downsview lands, a park on the northern edge of the city, to make Jesus Christ "the cornerstone" on which to build the future.

He contrasted two views which opened the millennium: Peace-seeking pilgrims at the last World Youth Day in Rome in 2000 and the September 11 terrorist attacks in 2001.

Questions about the direction of modern life, with its emphasis on productivity and secularism, will not go away, he said.

"The question that arises is dramatic: On what foundations must we build the new historical era that is emerging from the great transformations of the twentieth century? "Moved not by fear or violence but by the urgency of genuine love, they must learn to build, brick by brick, the city of God within the city of man.

"Allow me, dear young people, to consign this hope of mine to you: You must be those builders. You are the men and women of tomorrow," the 82-year-old pontiff said.

"The future is in your hearts and in your hands.

God is entrusting to you the task, at once difficult and uplifting, of working with him in the building of the civilization of love," he concluded.